The PLUVALOR System: Rainwater Harvesting for Whole House Reuse

This chapter applies to homeowners as well as professionals. With the advice herein contained and the assistance of tradesmen (materials suppliers, plumbers, masons), anyone can implement a rainwater harvesting and recycling system compatible to their needs and capabilities.

Note: This page is subdivided into many paragraphs which each constitute a hypertext link, intended to those who seek the answer to a precise question. That is the reason why, when reading the paragraphs in sequence, one will come upon redundancies.

About the PLUVALOR System

The PLUVALOR system is a rainwater harvesting and recycling system for whole house reuse, including potable water. The term PLUVALOR is a neologism that has double meanings in French. It comes from the words « rain » (PLUie) and « valorization » (VALORisation) combined in a word that suggests added value (« plus-value ») for the home. The suffix OR meaning « gold » is symbolical of water as a precious substance. Its intent is to suggest improved water quality through sustainable water management practices.

My research on the valorization of rainwater started in the 70’s at the Université Nationale de Zaïre in Africa. The research was completed at the Université de Mons-Hainaut in Belgium. The rainwater analyses performed during this research clearly showed that throughout its natural cycle, water is cleanest at the moment if falls from the sky, and this, in spite of atmospheric pollution.

Water’s natural acidity, due mainly to the CO2 in the air presents an advantage for water reuse. Indeed, the materials selected for the cistern neutralize this acidity, and in the process, water absorbs useful mineral salts. In a good cistern, we thus end up with chemically neutral water, weakly mineralized and naturally soft (without dissolved calcium and magnesium salts). From a chemical point of view, it is the ideal starting point for potable water preparation. For this, we need to eliminate bacteria with appropriate filtering. A cistern that is built as per PLUVALOR principles constitutes an artificial reconstitution of a natural rock cavity, where water conservation works well.

Reclaimed rainwater, stored and filtered in respect of PLUVALOR guidelines satisfies all domestic uses, including drinking water. Generally speaking, water quality in this system is far superior to mains water supply. Its purpose is therefore not to save city water, but to have of a better quality freshwater at one's disposal. Drinking filtered rainwater is a guarantee to good health.

The PLUVALOR system is not a manufactured off-the-shelf system. It differs greatly from rainwater harvesting systems that promote limited reuse of the water (i.e. for water-closets and exterior taps). It also differs from other whole-house rainwater reuse designs mainly on technical aspects but also because of its holistic approach to water management, a reflection on the philosophy behind the entire EAUTARCIE web site. This site takes a scientific and practical approach to sustainable ecological sanitation. 

Implementing the PLUVALOR System

The PLUVALOR rainwater recycling system cannot be improvised. The technical aspects developed below obviously apply to the PLUVALOR system. Those that resort to other systems must refer to their specific recommendations. Concerning PLUVALOR, more than 30 years of field experience has highlighted various problems that can easily be prevented, but that should be addressed when designing the home. Unfortunately, few companies are experienced with the PLUVALOR system. Consequently, design errors are numerous, which complicates the proper management and reuse of rainwater.

To start off, in France, the PLUVALOR system is strictly forbidden. The law obliges cistern materials to be inert to water. Therefore, the use of concrete cisterns (which neutralize water acidity, thus reacting chemically to water) is forbidden. Domestic use of rainwater collected within «inert» cisterns, i.e. plastic cisterns, is only authorized for exterior tap use. The authorities discourage even the use of rainwater in standard water closets (unless the water is preconditioned by UV irradiation). Note: in plastic cisterns, rainwater remains acid and rapidly become putrid. This is absolutely not the case in concrete cisterns.

The authorities in Belgium are more pragmatic and especially more in line with the most recent scientific data. The legislation that, in fact, has integrated the notion of sustainable water management, has placed this small country at the state-of-the-art in matters of rainwater reuse. In a country whose population reaches 10 million, more than 700 000 people use rainwater for their personal hygiene (bath, shower, tooth brushing) and of those, more than 100 000 have been drinking it for years. Rainwater harvesting and reuse has contributed to the ongoing reduction in water consumption in Belgium. Wallonia (south region of Belgium) detains the absolute water savings record: 114 litres per day per person.

To visualize the general schematic of a PLUVALOR system, click here.

After careful reading of the present documentation, a discussion is highly recommended with your architect, your contractor and your materials supplier.

Cistern Dimensions

The cistern dimensions are calculated with respect to the roof area servicing the cistern. Do not size the cistern on the basis of the number of inhabitants, nor the expected household consumption. These criteria only come into play when the house disposes of an extra large roof.

Within measure of the site’s potential, when designing a home, it is preferable to choose a one-story instead of a two-story house to increase the roof area available for rainwater harvesting. Obviously, all roof slopes should be connected to the cistern.

For each 100 m² (e.g. 10m x 10m) of roof area measured horizontally, calculate a cistern capacity of at least 15 m³. A 5x10m house will thus have a 7 5OO-litre (7 m³) cistern; a 10x20m home will have a 30 000-litre (30 m³) cistern. You can obviously round out the figures, preferably upwards.

When building the cistern, it will have two compartments, the first for sedimentation (or decanting) will represent 20% of the total volume, and the second for storage, representing 80%. Note: the cistern volume must be calculated up to the level of the overflow.

All roof water arrives in the cistern’s sedimentation compartment. Its overflow spills into the water storage compartment. To prevent the passage of floating impurities, the sedimentation basin’s overflow must be a trapped overflow, i.e. equipped with a protective skirt or an inverted elbow pipe.

When using prefabricated cisterns, consider at least two tanks, the first and smallest to be used for sedimentation, and the larger one for storage. The cisterns are to be interconnected with piping at the top.

Cistern Materials

Try to avoid plastic and metal cisterns. To properly neutralize rainwater’s natural acidity, choose concrete, standard masonry or limestone.

Considering the fact that plastic cisterns (PVC, polyethylene, polypropylene) are less expensive and more easily transportable than prefabricated concrete cisterns, it would be interesting to experiment rainwater storage in a plastic cistern, but after the water has passed through a small concrete cistern to neutralize it. For this, you could place a small concrete cistern for sedimentation with the overflow spilling into a plastic tank for storage. You could even consider putting limestone or limestone granules in plastic cisterns to neutralize the water. This last solution however makes maintenance difficult, i.e. to properly remove the sludge resulting from sedimentation when a cleaning is required.

Note that all cisterns, be they concrete or plastic must be placed underground for whole-house reuse of the water. Some German manufacturers recommend putting 1500 to 2000 litre plastic tanks in a basement for water storage. In these cisterns, without proper water neutralization, the water rapidly becomes putrid due to the temperature fluctuations. The water can at best be used for laundry purposes.

To prevent unwanted underground water infiltration within the cistern, it is preferable to waterproof the outside of the tank with an appropriate membrane. The cistern’s inside should be covered with a cement plaster or a polymer-modified waterproofing system containing cement. This is important to neutralize the water’s acidity. Avoid synthetic coatings that do not. Watertight coatings composed of polymer-modified cement can neutralize rainwater. However, their long-term performance is unknown. The plastered finish must be smooth to prevent bacterial growth and make cistern maintenance easier. Generally, a cement plaster coating is quite satisfactory and adequately water tight. Some cisterns still exist in old fortresses, built of limestone masonry and lined with a limestone mortar and yet still function perfectly after many centuries.

Quality of Concrete

Many potential users want to know if any and all concrete is appropriate for rainwater storage planned for human consumption. What comes to mind are toxic residues that may come from the use of «substitute fuels» (various wastes) that can be burned in cement factory furnaces. This is not a problem. Consider that Portland cement used for concrete is made at a temperature of 1700°C which no organic molecule, toxic or not, can resist. Any heavy metal components will be incorporated in the end product, but in silicate and oxide states that are practically insoluble in water. 

When monitoring the water quality in cisterns, we have never come upon a heavy metal content greater than that which is prescribed in potable water standards. This is unfortunately not the case for some mains water supply in which a temporary exceedance is possible and even accepted by law.

Prefabricated Tanks

For prefabricated cisterns, a cylindrical or oval shape is normally imposed by the manufacturer. Concrete cisterns of this type are quite adequate, but must sometimes be adapted to the rainwater system. This may involve correcting the inside surface roughness by the addition of a smooth thin cement mortar, or introducing some sort of pit or sump at the bottom, or even enlarging the manhole access, and eventually installing a ladder to the bottom. Also consider replacing the concrete cover plate by a lighter reinforced metal hatch.

Cistern Maintenance

For maintenance purposes, it is useful to install ceramic tile at the bottom, and only at the bottom. The floor should thus be lightly sloped towards a low point, ideally a catch basin that will accommodate a submersible pump. Without such a set-up, the cleaning of a cistern can become a real chore.

The access hatch must be sufficiently wide for a stout person carrying a bucket. Ideally, have a ladder installed on the wall closest to it. The hatch must be light, but solid. A concrete cover is too heavy to manipulate. Prefer reinforced steel or aluminium, with a recessed handle or holes for easy opening of the cover with a hook.

Through the cistern’s continued use, sediment tends to deposit on the cistern’s floor. This comes from solid impurities (dust, roof moss, etc.). In most cases, this « sludge » presents no inconvenience. When there is too much of it, anaerobic fermentation can provoke odour and a yellow colour to the water. More often than not, the use of an aquarium aerator with its bubble diffuser will promote the water’s aeration and eliminate the problem within days. If the odour persists, you must proceed to the cistern’s maintenance. Unless it’s an emergency, one waits for a dry spell, when the water level within the cistern’s storage compartment is low. To start, use the submersible pump to remove the water. Leave about 10 to 15 cm of water on the floor for a first cleaning. The walls must be brushed down with a hard bristle brush. You can also use a high pressure cleaner (e.g. «Kärcher»). In this case, it is not necessary to leave water at the bottom for the first cleaning. The dirty water is removed by putting the submersible pump in the catch basin. During this procedure, scrape the cistern’s floor towards the low point just as you would clean the floor tile of your kitchen or bathroom. That is the reason I recommend tiling the floor of the cistern, and only the floor. A last clean water rinse is necessary. City water can be used for this purpose, if available. Finally, remove the rinse water with the sump pump. After this cleanup, use the pump to transfer the water from the sedimentation basin to the now clean storage basin. To prevent transferring any sediment, be careful not to pump the contents located at the bottom of the sedimentation basin. After that, repeat the cleaning operation for this tank.

Maintenance Frequency

The maintenance frequency varies from one set-up to the next and it is therefore impossible to define. Purpose of the maintenance is to remove the sediment that inevitably deposits on the cistern’s floor and which may give rise to parasitic fermentation and the consequent odours. The rate at which the sediment accumulates depends on the region’s atmospheric pollution (for dust), the roof type, and the quality of the set-up upstream from the cistern’s storage compartment.

A good sand filter placed between the roof gutter’s main downspout and the sedimentation basin will substantially delay the forming of sludge. Fortunately, in most cases, a well-conceived sedimentation basin equipped with an appropriate trapped overflow that prevents the passage of floating impurities will suffice.

I know of some installations that still function perfectly, yet have not been cleaned up in the last twenty years, whereas others need a cleanup every two years. A good indication of a need for maintenance is when odours appear at the faucets. If these are not eliminated after a few days of aeration with an aquarium aerator (maximum of 10 to 15 days), a thorough cleanup is required. Please note that odours may also appear when a filter is blocked at the outlet of the water pump set-up: this should be checked first.

Read further on this subject in the paragraph odours in the cistern.

Cistern Equipement

For large cisterns (greater than 10 m³), it is recommended to install a sealed light fixture at the cistern’s ceiling, controlled by a light switch (with an indicator lamp) that would be located within the house.

The pipes interconnecting many cisterns must be flexible enough to absorb potential terrain or soil movement. The overflow that spills out from one cistern to the next will again be a trapped overflow to prevent the transfer of floating impurities.

The inlet pipe to the home’s pump system must have a one-inch minimum diameter, be flexible and equipped with a floating strainer so as to prevent transfer of sediment from the bottom and floating impurities from the top of the storage tank.

When using reverse osmosis to produce potable water, also include a return pipe to the cistern’s sedimentation tank for the backwash of the reverse osmosis unit’s membrane.

Include a tube feed to the bubble diffuser for the aquarium aerator. It consists of a flexible plastic tube of less than 8mm diameter. An aquarium aerator is optional, but it may come in useful if ever odours are a problem in the water. Even if it were not included, it would be wise to plan for its eventual addition, including the electrical outlet and a control switch with indicator lamp within the house. In order to properly inspect its operation, the bubble diffuser should be located at the bottom of the cistern, just below the access hatch.

Never connect the cistern overflow to a sewer. Most laws in fact forbid this. A cistern’s overflow will rarely serve if the cistern is in continuous use. Thus, a simple absorption pit or underground dispersion system [2] will suffice to receive excess water. You can find manufactured overflows on the market. It is also important to cover the overflow’s outlet with an appropriate screen to prevent intrusion of rodents and frogs into the cistern.

Upstream From the Cistern

Water running down the roof must be filtered or decanted. To protect the home’s filtration equipment, a sand filter is the least expensive, and very efficient. Manufactured concrete filters are also sold on the market.

You can also find sediment filters having a porosity of 100 microns, which are to be placed under every gutter downspout. These are very practical, but need to be cleaned out regularly.

Leaf interceptors that go into the gutter downspout can also be found on the market. These tend to block frequently, provoking substantial water loss.

In warmer countries with extended dry rainless periods and concurrent dust-carrying winds, an additional sedimentation pit could also be considered upstream from the main cistern and downstream from the main feed from the gutter downspouts. Such a pit will have a volume of about 200 to 300 litres at the bottom of which the coarser particles will settle. The pit will be covered to prevent intrusion of rodents and frogs, and a trapped overflow with inverted elbow will again be provided to prevent floating impurities in the pit from entering the main cistern’s sedimentation compartment.

Gutters and Downpipes

Appropriate materials include zinc, galvazed of enemailed steel, PVC and glazed clay. Avoid aluminium. Copper and lead are quite inappropriate. These are very soluble in an acidic environment (rainwater that falls on the roof is always acidic) and are poisonous. In doubt, it is better to have the cistern water analyzed for toxic metal content. If you already have copper or aluminium gutters, have the water analyzed in accordance. If the metal content exceeds potable water standards, this does not mean that the water is unsuitable for other than food purposes. However, for the production of one’s drinking water, it is necessary to resort to reverse osmosis. This technique eliminates all risks due to heavy metals.

Zinc, Lead and Copper in Rainwater

In cistern water, the highest heavy metal content (in Europe) to be found is zinc. This element can come from gutters or zinc roofs. Fortunately, zinc is not very soluble in an acidic environment (e.g. like rainwater’s pH). We have never measured zinc contents exceeding 1700 µg/l (micrograms per litre) in our cistern water quality controls. The admissible content for zinc is around 5000 µg/l. Some people can be sensitive to zinc and even develop an allergy. Fortunately, this affliction is rare, although its frequency is increasing due to the general weakening of the population’s immune system.

It so often happens that certain roof elements (chimneys, skylights, solar panels, etc.) are waterproofed with lead flashing. The water that trickles down the roof comes into contact with such flashing for a very short time. One must obviously avoid lead gutters because water can eventually stagnate and dissolve some of the metal. In certain analyses that we performed on different set-ups, we never measured a lead content exceeding the potable water standards. The measured content was systematically ten times less than the accepted standards.

Copper gutters service some older houses. When restored, if they are not replaced, these must be properly repaired to eliminate any water stagnation, primary source of verdigris or copper corrosion. For aged copper gutters and roofs, rainwater cistern water must be analyzed for its copper content. If this exceeds 1 mg/l, a microfiltration system is unsuitable for potable water production and one must resort to reverse osmosis, which eliminates copper ions in water. For non-food purposes, a weak copper content (up to a few milligrams per litre) is not inconvenient. In fact, it is a bactericide.

In light of the above, if in doubt, you can always have the cistern water analyzed. Under such circumstances, it is better to choose a reverse osmosis system (a little bit more expensive) instead of microfiltration when considering potable water production. Comparison of the two systems will be found on the Potable water production page. Reverse osmosis will eliminate any heavy metal to be found in the cistern’s water. I must insist on the fact that a heavy metal content that exceeds recognized standards is only dangerous if ingested in great quantities. Whatever quantity one accidentally swallows in a bath, shower, or while brushing one’s teeth is much too weak to constitute a health risk. Let me also insist on the fact that most supply water, measured not at the production plant, but at the homeowner’s faucet, contains more heavy metal than can be found in the reclaimed water of a rainwater cistern.

Gutter Design and Maintenance

When falling leaves are expected on the roof, a removable protective screen should be placed over the exposed gutters. To avoid intrusion of dead birds in the cistern, also place a screen in the gutter above each downpipe. Please note that these screens require frequent inspections, every two months, and even more frequently in the fall. They are easily blocked which can provoke gutter overflow. Leaf interceptors are also useful but also need regular inspection as they tend to block frequently, provoking substantial water loss.

In addition to regular gutter and downpipe inspections, the gutters need to be cleaned twice a year, before and after winter. When designing a home and garden, you should consider easy access for ladders.

The first rainfall following an extended dry spell is liable to carry a certain quantity of dust into the cistern. This dust will settle as sediment. To delay this process, some recommend the introduction of a tilt type first flush diverter system at the downspout. It consists of a 1-meter segment of gutter connected to a float placed in a 200-litre container. When the container is empty, the float would be in its low position. The gutter segment is thus sloped towards the container and at first rain, the water is diverted into the container. As the container fills, the float lifts, and so does the gutter which eventually tilts in the other direction, towards the cistern inlet.

A good handyman can build such a system. However, it is not essential. The problem is that the container must be emptied at the right moment: not too early, nor too late. When it’s emptied systematically, water loss is not negligible. When one forgets to empty it, the system fails to do what it should, and the first rains, loaded with dust go straight to the cistern. I consider that a good decanting system is sufficient to avoid a too rapid accumulation of sediment. In addition, the system needs no surveillance, as would a tilt type diverter system.

Alternatively, a better-designed system is available on the market as seen on the Rainharvesting web site at http://www.rainharvesting.com.au/first_flush_water_diverters.asp.

Roof Materials

The best materials are clay tiles (preferably enamelled, to avoid growth of moss), natural slate, zinc and glass. An exposed flat concrete roof is suitable as long as it is not used as a lounging area. Synthetic slates [3] are tolerable, as are corrugated galvanized steel or corrugated plastic or fibreglass. Avoid copper, aluminium or synthetic imitation tiles, and avoid asphalt shingles.

Comment:

The (European) press occasionally points out a too high zinc content in rainwater. One immediately thinks of zinc gutters and roofs (at least in Europe). However, as these readings were taken on rainwater collected on sidewalks or garden alleys, the higher than usual zinc content is probably due to phytosanitary products (pesticides and herbicides) used in the urban environment.

In any event, zinc is insoluble in an acidic environment. Rainwater on a roof is always acid, even in the absence of pollution. Numerous analyses were made of water in rainwater cisterns, in collaboration with Professor Paul Vander Borght of the Université de Liège . The readings indicated an average zinc content of 500 µg/l (micrograms per litre). The admissible concentration for potable water is 5000 µg/l. Therefore, the harvesting of rainwater from a zinc-covered roof does not constitute a problem.

Green Roofs and Flat Roofs

Forget the green roofs, unusable for domestic water reuse (and that's not forget the long term waterproofing problems, and the extra loads requiring an appropriate, more expensive structure, thus more expensive). A green roof reclaims little water for the cistern, only that of major rainfalls. In addition, the water will be loaded with impurities: humic particles giving the water a brownish colour, and lots of bacteria.

A flat roof is ok for water harvesting, on two conditions :

1. The roof materials must comply with the criteria described herein : the recommendation against asphalt shingles also applies to asphalt or tar-based roof membranes.
2. The roof must not be used as an accessible terrace for lounging or other activity.

Wood Shingle Roofs

In spite of their rustic appearance, wood shingles (hemlock, cedar or other) do not represent a good solution for rainwater harvesting. Comparatively, on a tile roof, water will runoff much quicker than on a shingle roof. By its inherent roughness, wood retains a certain quantity of water that is than lost to evaporation, never arriving into the cistern. This type of water loss is estimated at 5% of total precipitation. If the roof is already a bit small with regards to the household’s water needs, this is not a negligible quantity.

Wood’s inconvenience is mainly due to its negative impact on the harvested water’s quality. The water colour becomes lightly brown or yellow due to the presence of essential oils diffused by the wood. This water will at the outset be laced with organic matter in suspension, a bonafide breadbasket for bacteria. Fortunately, such bacteria are not pathogenic, but it can be annoying. One must wait 5 to 10 years before seeing the reclaimed rainwater clear and clean.

Asbestos roofing

Artificial slate roofs sometimes contain asbestos, but this does not constitute a major inconvenience for rainwater reutilization. Asbestos is only toxic by inhalation. As far as I know, there is no proof of toxicity through ingestion.  But it is still best to avoid this type of roof for new housing. Those who fear even the ingestion of asbestos fibres (which will not be filtered by ceramic based microfiltration) will no doubt resort to reverse osmosis for their drinking water production.

Cistern Location

To insure good water conservation for whole-house reuse, a cistern must absolutely be put underground. It can be placed under a terrace. A waterproofed room at basement level can also be used as a cistern, as long as this is not under part of the house, rather under a garage or a building annex for example. In an existing construction, it can be placed in the yard under a pergola for example (the pergola being optional!). Decorative landscaping can be done above the cistern with plants, stone pavers, etc. Note that grass planted above a cistern will yellow much quicker during dry spells.

In addition, the roofs of all annexes like the garage, greenhouse, garden canopy, firewood shelter, etc. should also be connected to the cistern.

Also consider ease of access and maintenance to the cistern. To avoid lighting your way down the cistern with a portable lamp, potentially dangerous when your feet are in water, consider providing electric power to feed sealed lamp fixtures at the cistern ceiling. This power will also feed the aquarium aerator. The control switches for these should be within the house and should come equipped with indicator lamps.

Well Pump System

The pump’s purpose is to pressurize and inject water from the cistern in the house’s plumbing system. In Belgium, this is called a hydrophor pump system. A standard home requires a pump of at least 350 Watts. Piston pumps are very good, but relatively expensive. In addition, they require a large pressure tank placed after the pump to insure a more stable operation: normally 200 litres. Less expensive centrifugal pumps also work fine: in their case, a 25 to 30-litre pressure tank suffices. A pressure tank, even a smaller one, is indispensable for those who resort to reverse osmosis. One can still find pump systems without pressure tanks. As soon as a faucet is opened somewhere in the house, the pump turns on. This is not the case of a system equipped with a pressure tank. With a pressure tank, the pump will function less often, use less power, and last much longer.

Bigger Piping

The plumbing systems inside the house require careful attention. For mains water supply, a half-inch pipe diameter is fine. When pumps and pressure tanks come into play, the pipe diameter needs to be bigger, preferably one inch in diameter. This is to avoid pressure loss when more than one faucet is turned on. City water pressure is supported by a load of hundreds if not thousands of litres of water with a compressibility that easily absorbs pressure fluctuations. That is not the case for a residential well pump system.

Double the Piping or Not?

Let us insist on the fact that contrary to the usual recommendations in the industry, a PLUVALOR rainwater harvesting and reuse system does not require doubling the piping network within the house, i.e. one for rainwater, and the other for city supply water. The system is perfectly adapted to existing plumbing set-ups, without transformations. In certain cases, when roof area is insufficient to insure plentiful water supply, doubling the pipes becomes necessary. (See next paragraph).

When choosing rainwater harvesting systems other than the PLUVALOR system, it is generally recommended to double the pipes in the house. The systems recommended by most merchants are expensive and less efficient. If a merchant is not familiar with the PLUVALOR system, one may end up buying expensive equipment of dubious utility.

Rainwater with City Water

When the roof area is limited and harvested water does not cover the household needs, one can consider a mixed-use plumbing set-up in the home. In this case, an interesting solution is to connect the water-closet(s) and exterior taps to city water, and to feed the rest of the house with reclaimed rainwater. This comment is only applicable to those with a PLUVALOR system.

Water supply and distribution companies recommend doubling the plumbing systems. The rainwater reuse recommended by these is limited to watering the garden and feeding the water closets. Some specialists will even accept the use of rainwater for the laundry, on the condition certain measures are taken. That is certainly not the objective of the PLUVALOR system, which is the result of a totally different philosophy. (Users who adopt the PLUVALOR system express a way of thinking that goes beyond an institutionalized system of irresponsibility, as they become responsible managers and producers of their own water.)

Some will be tempted to place a set of valves to feed the house in turn from the cistern or the city water. From a technical point of view, this is a rational approach [4], and is certainly very practical. But the water supply and distribution companies will not accept it. Some companies accept the connection of one or the other source to the house’s plumbing network, as long as this is done with a flexible and detachable pipe. In any case, it is absolutely necessary to include a check valve (non-return valve) right after the water meter.

Another technique would be to install a pipe from the water meter’s outlet to the cistern: this could even be a simple flexible garden hose. Make absolutely sure however that the water meter’s connection to this pipe is situated above the cisterns overflow level.

IMPORTANT! In all cases, make sure that the cistern water cannot get into the city water network.

Before the cistern goes dry, one will put in a bit of city water. Thanks to the cistern’s content, the city water introduced into the cistern will be somewhat improved in quality due to its dilution by better quality rainwater.

The Problem with Chlorine Bleach

Avoid putting bleach into the cistern. (Read more on this subject at the chlorine page.)

In a cistern’s stagnant water, and notably in the sediment at the bottom of the decanting basin, lots of bacteria – mostly harmless – thrive, conveying to the water a biological equilibrium that varies from season to season. Like the wine in a barrel, the cistern’s water «lives» and changes with the seasons. Introducing a biocide like bleach gravely perturbs this equilibrium. The chlorine found in bleach indiscriminately kills all bacteria, which then break up, discharging their genetic matter into the water. The medium becomes oxidant, thus favouring the advent of bacteriophagic viruses that feed on the destroyed bacteria’s genetic matter. Unless one resorts to reverse osmosis for drinking water, these viruses will not be adequately filtered and may end up in the drinking water. Once absorbed into our body, these viruses can mutate and produce pathogenic strains. The water having become oxidant because of the chlorine makes matters worse by decreasing the electronic activity of the liquids within our body. Generally, the chlorine weakens our immune system, as much by ingestion as from external use. Infants and young children are particularly sensitive to chlorine. After having switched over from city water to rainwater, many families have observed a reduction, and even the elimination of allergies. For an infant, the daily bath in chlorinated water is far from beneficial.

In exceptional situations, you can resort to bleach in order to clean a cistern, especially if the tank previously contained sewage or liquid manure. When reclaiming old septic tanks or pig manure tanks for rainwater cistern purposes, it is better to disinfect these and apply a smooth cement based plaster. The cleaning must be done with a hard bristle brush, otherwise with a high-pressure cleaner (e.g. «Kärcher).

When There is Not Enough Rainwater

When the roof area is too small to provide sufficient rainwater for the household, a rational solution is to connect the water closet and the garden hose or similar outlets to city water, and connect the rest of the house to the rainwater cistern. This reduces the rainwater needs by 30 to 40%.

The basic thinking behind the PLUVALOR system is not to save city water by harvesting rainwater, but it is rather to provide better quality water (naturally fresh) and preserve one’s health by the use of non chlorinated and weakly mineralized water. High quality rainwater is thus reserved for more noble uses (drinking, cooking, personal hygiene) and lesser quality city water will be used to feed the water closet (if one insists on keeping one, against all environmental logic) and for garden watering.

With a water level indicator in the cistern, you can easily determine when it’s time to change from rainwater supply to city water supply, and vice versa. Thus, one installs a tank level gauge in the cistern connected to a water level indicator in the house. Even more efficient would be to install a water tank level sensor in the cistern and the corresponding water level indicator displayed in the kitchen for example.  Such water level sensors are usually sold by the fuel tank industry and are becoming increasingly available in the rainwater harvesting industry. Wireless models are also available. They cost between 50 and 100 €. (Hi-tech lovers can even resort to ingenious systems proposed on the market, whereby the management of the city water/rainwater feed is fully automated. This solution remains debatable in light of the extra expense.)

The mains water supply should be controlled by a solenoid valve. When the valve opens, the city water will flow into the cistern until a shut-off is triggered by a float switch (similar to the float in a toilet’s flush tank) to limit the quantity of city water introduced into the cistern. It is unnecessary to fill the cistern with city water as is recommended in certain tank top-up systems on the market. A bit of city water is enough, until the next rainfall.

In certain countries, even European, more than one water supply source is authorized to feed the home’s plumbing system. The only restriction is that there be a check-valve placed right after the water meter. This protects the city water network from potential contamination from a non-potable source. From that point on, it is clear that a house can be serviced by two separate valves, one at the city water meter, the other at the cistern. It is a simple, practical and efficient solution. Here again, when the roof area in insufficient to cover the household’s rainwater needs, you should connect the water closet and garden hose to the city water on a permanent basis.  

How to Deal with a Rainwater Harvesting Equipement Supplier?

Merchants who sell equipment for home water management must comply with the law. In France for example, it is compulsory to use potable water for every single use in the house. Short of encouraging civil disobedience, I must point out the incoherent laws and inadequate water legislations in existence. In some cases, the techniques recommended AND imposed, like disinfection by chlorination or UV irradiation can be justifiably considered as a breach on public health.

When consulting a supplier, you will often hear recommendations on placing activated carbon filters and especially UV lamps in the household’s water network for all water uses. Don’t be too easily impressed by a « green » set speech about rainwater harvesting when the supplier or merchant recommends using rainwater for the water-closet, garden and laundry. You can be certain he ignores the latest scientific developments about rainwater recycling, or for personal reasons, he prefers not to acknowledge the sustainable water management principles of whole-house rainwater reuse. He will have you spend lots of money on an inappropriate solution. And I am not even speaking of the totally inadequate environmental approach of the industry.

Activated carbon is called upon to eliminate micro-pollutants (pesticide residues, hydrocarbons) and cistern odours. For sanitary use in a rainwater harvesting system, the experience of thousands of households has shown that this type of filter is not necessary. Odours are controlled – in the great majority of cases – by the aquarium aerator recommended herein. This equipment does not even have to work all the time. Many users never have to turn it on.

Certain merchants also recommend filtering all water used by the household down to 5 microns, even to 1 micron. This is not really necessary, while at the same time being expensive. One and 5-micron filters tend to block up very quickly. They require frequent maintenance without proven practical use. On the contrary: the weaker a filter’s porosity, the greater the pressure loss and the weaker the water flow will be. In practice, water filtered at 25 to 30 microns, followed by a second filtering down to 10 microns satisfies all non-food requirements. A 10-micron filter provides clear water. Such a filter placed in the home’s plumbing network filters a considerable amount of impurities. In some city water fed homes for instance, a 10-micron filter placed right after the water meter is saturated with impurities within two weeks.

With the instructions and recommendations given on this website, one can successfully implement a PLUVALOR system without needing to consult a rainwater harvesting «specialist». Concrete tanks, pumps, well pumps systems, 25, 10 and 5-micron filters and activated carbon ceramic filters are all available on the market. Be careful not to get influenced by salesmen who know nothing of the PLUVALOR system. It remains, nevertheless, that these salesmen have the right equipment for your needs.  I must insist however: for rainwater, no UV lamp is required to disinfect the water: a ceramic filter suffices. You absolutely do not need a water conditioner to filter out calcium, nitrates, etc. nor filters against iron and/or heavy metals. You must never forget that these filters were designed not for rainwater, but for city water.

Most rainwater harvesting suppliers are ignorant of all the possibilities of whole-house reuse rainwater. They will propose expensive equipment unsuited to the PLUVALOR system. Therefore read very discriminately all literature on rainwater.

Important notice:

The EAUTARCIE website is not tied to any commercial activity.

The Problem with UV Water Treatment

The purpose of UV water sterilization is to kill the last bacteria that may have escaped filtration. The bactericide efficiency of UV lamps requires that at each use, a certain quantity of water must be wasted to compensate for the flow of « non-disinfected » water during start-up of the lamp. The problem with UV lamps is elsewhere. Numerous observations made on plants watered with sterilized water tend to indicate a negative impact on health.

In water’s absorption’s spectrum, there is a wide band in the ultraviolet. This means that almost all energetic ultraviolet photons are absorbed by the aqueous medium. This results in a grave disruption of the water molecules’ vibration intensities that leads to the destruction of the supramolecular polygenic structures of the water medium. In fact, these polygenic structures define water’s biological properties. We do not know exactly what effect irradiated water has on the human body, but by extrapolating from irradiation’s effects on living matter, the precautionary principle should dictate that is it preferable not to irradiate water for human consumption. Many of my correspondents are worried of the effects of UV sterilization on their health. Until further scientific data is obtained on the matter, you can read my personal opinion on the matter.

In addition, water usage for other than food need not be sterile. Based n the experience of thousands of households using this rainwater harvesting system, 10 micron filtering does not appear to pose a health problem. For drinking water, (2 to 3 litres per person per day), a microfiltration system (see chapter on Potable water production) will provide a water quality that complies with the strictest standards.

Important notice. The use of the PLUVALOR system is strictly forbidden in French public buildings. The law permits the bureaucrats to go so far as to impose UV sterilization to harvested rainwater that is used to feed water closets. My opinion on this issue: it is the government scientists’ responsibility to properly evaluate the relevance of this measure compared with the costs and health risks also involved by the use of chlorinated water.

Closing Remarks

To Resume my private opinion on the prohibition of this system:

Domestic rainwater harvesting and reuse based on the PLUVALOR concept is a very personal choice that is strictly a private affair. In this sense, imposing (instead of recommending) rules on water quality within the home is unconstitutional. It is an unacceptable breach on a citizen’s private rights. While respecting others’ rights, the decision to become a responsible manager and producer of one’s own water remains one’s own inherent right.  

It’s strange that discussions around one’s right to possess potentially dangerous drugs and narcotics for personal use is accepted in public debate whereas such debate is swept aside when it comes to imposing what water one can drink in one’s own home, when this water can be suspected harmful to one’s long term health.

To continue reading, go to page on Rainwater Quality

To view an incorrect rainwater recovery design, click here

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[2] It’s a simple hole dug in the ground with a volume that must be increased proportionately to the soil’s imperviousness. Considering a 10 m³ cistern and a permeable soil, a 1-m³ hole filled with broken bricks (waste material often found on site after construction) and covered with 15 cm of earth will suffice.

[3] The asbestos contained in some roof materials (Eternit) is really only harmful by inhalation. Its ingestion doesn’t seem to have a health impact. 

[4] In reality, by taking precautionary measures, the probability of introducing rainwater in the public water distribution network is very weak. It is rare that a well pump system can produce a higher water pressure than that of the city water. A proper check-valve placed after the water meter is a sufficient guarantee against such an incident. To avoid all risks, I recommend separating the city water fed plumbing circuit from the cistern fed circuit.