Estas páginas están en proceso de traducción por voluntarios, cuyas lenguas maternas no son el español.
Nuestro objetivo es ofrecer una información útil para el público hispanohablante. Para mejorar la calidad de esta información estamos buscando colaboradores voluntarios para corregir, o encargarse de la traducción de otras páginas. Los traductores siempre tienen la posibilidad de eligir lo que quieren traducir.
La propuesta de colaboración puede ser dirigida a Joseph Országh
Para ver el esquema general del sistema PLUVALOR, pincha aquí.
El texto de esta página se publicó por primera vez en francés en www.eautarcie.com: en 2003
The original text has since been adapted in English and was first published on this page at www.eautarcie.org: 2017-02-26
El sistema de recogida de agua de lluvia PLUVALOR no puede ser improvisado. Los aspectos técnicos desarrollados a continuación son para aplicarse, obviamente, al sistema PLUVALOR. Aquellos que opten por la aplicación de otros sistemas deberán seguir otras recomendaciones. En lo que se refiere al sistema PLUVALOR, tras más de 30 años de experiencia sobre el terreno se han detectado varios problemas que pueden evitarse fácilmente, pero deben abordarse durante el proceso de diseño de la vivienda. Desafortunadamente muy pocas compañías tienen experiencia con la aplicación del sistema PLUVALOR. Como consecuencia, los errores de diseño son numerosos y complican la correcta gestión y utilización del agua de lluvia.
Recordemos que una cisterna de agua de lluvia para el uso doméstico no es otra cosa que la reconstrucción artificial de una cavidad rocosa subterránea en la que el agua almacenada se conserva bien. Para la buena conservación la temperatura debe mantenerse constante (y este será el caso de una cisterna enterrada), y el agua deberá poder ser neutralizada por las paredes de la cisterna. Esta condición se cumple en las cisternas que están realizadas con hormigón o con mampostería y recubiertas con mortero de cemento. Gracias a la neutralización el agua se carga ligeramente con sales minerales (sobre 50mg/l). Si pasamos por alto estas condiciones el agua de la lluvia puede volverse putrefacta y maloliente. Este es el caso de las cisternas de plástico o metal, y también de las cisternas que no están enterradas.
Para ver es esquema de funcionamiento general del sistema PLUVALOR, pinche aqui.
Para el tejado, los materiales más convenientes son aquellos que son menos susceptibles de alterar la calidad del agua de lluvia. Esto incluye Tejas de cerámica (preferiblemente esmaltadas, para evitar el crecimiento de musgo), tejas de hormigón, pizarra natural, acero inoxidable, zinc  y vidrio. Pizarras sintéticas son tolerables, al igual que el acero galvanizado corrugado o plástico corrugado o fibra de vidrio.
Para los canalones y las bajantes, los materiales apropiados son el zinc, el acero inoxidable, el acero galvanizado, el PVC y otros plásticos, y cerámica esmaltada.
Cuando quieres instalar un sistema de recuperación de agua de lluvia con un tejado y unos canalones existentes que no presentan los materiales convenientes la filtración se vuelve más difícil. Esto no significa que sea obligatorio remplazar los materiales defectuosos, pero hay que realmente considerarlo cuando ha llegado el momento de reemplazar un tejado antiguo o unas bajantes que fallan. Mientras tanto, dependiendo del tipo de sustancias indeseadas a las que el agua de lluvia está expuesto vamos a necesitar elegir el sistema de filtración más adecuado incluyendo el sistema de cañerías de la casa. En caso de gran cantidad de impurezas solidas o bacterias los filtros tienden a abrirse más rápido. Esto implica un reemplazo más frecuente de los componentes filtrantes, lo que significa que el agua así obtenida puede llegar a ser más cara que el suministro de agua de la red.
Hay que evitar los tejados y canalones de cobre, de plomo y de aluminio. Estos metales (excepto el aluminio) son solubles en el medio ácido (la lluvia que cae sobre el tejado es siempre ácida), y son tóxicos. En caso de duda sobre una instalación existente va a ser mejor hacer un análisis del agua de la cisterna. Si el contenido excede los estándares de agua potable se puede considerar un uso seguro del agua de lluvia para fines no alimentarios, con un filtro primario ( de 35 a 10 micras). Sin embargo, para la producción de agua potable habrá que recurrir a la osmósis inversa (en lugar del sistema de microfiltración).
A pesar de su aspecto rústico las tablillas de madera (alerce, cedro u otros) no constituyen una buena solución para la recuperación del agua de lluvia. En sus rugosidades la madera retiene una cantidad de agua significativa. Tras una llovizna, el agua fluirá más rápido hacia la cisterna sobre un tejado de tejas que sobre un tejado de madera. El agua retenida en las asperezas de la madera terminará evaporándose y no llegará a la cisterna. Este tipo de pérdida puede estimarse alrededor del 5% de las precipitaciones totales. Si el tejado del que disponemos no es muy grande en comparación con las necesidades del hogar, esta cantidad está lejos de ser despreciable.
Pero en los tejados de madera el inconveniente principal se debe al deterioro de la calidad del agua recuperada. El color del agua se vuelve marrón o amarillento debido a la presencia de aceites esenciales aplicados sobre la madera. En esta agua habrá además, sobre todo al principio, una suspensión de materias orgánicas. Estas constituyen un verdadero medio de cultivo para las bacterias. Afortunadamente estas bacterias no son patológicas, pero pueden ser molestas. Habría que esperar entre 5 y 10 años para que el agua se volviese incolora y relativamente limpia.
Es preferible evitar los materiales sintéticos como el alquitrán o las membranas bituminosas que pueden conferir un gusto, olor y color desagradables al agua, e incluso liberar los hidrocarburos aromáticos potencialmente cancerígenos en la cisterna. En presencia de estos materiales la colocación de un filtro de carbono activode gran capacidad se impone para la producción de agua de calidad inofensiva (no potable). Sin embargo, varios informes sugieren que las tejas de asfalto y grava, denominadas «shingles», son convenientes para la recuperación del agua de lluvia. Esta conclusión de apoya en un estudio estadounidense  que sugiere que la configuración y la composición de estas tejas reduce sustancialmente el escurrimiento de hidrocarburos aromáticos e incluso de metales pesados.
De cualquier manera, en los tejados planos con alquitrán y asfalto, con el paso de los años, se produce un fenómeno de envejecimiento y el olor en el agua recuperada en ellos finalmente desaparece. Desafortunadamente para el agua de lluvia este hecho puede tardar varios años. Por otra parte, esto será una señal obvia de que el material está llegando al final de su vida útil y que necesitara ser remplazado próximamente.
I am led to understand that certain types of synthetic waterproofing are commonly used in commercial, institutional and industrial buildings, and appear to give good results in terms of rainwater quality. These include Polyvinyl Chloride (PVC), Ethylene Propylene Diene Monomer (EPDM – an artificial rubber), and thermoplastic polyolefin (TPO). These can be successfully adapted for housing : one of my correspondents is quite satisfied with his EPDM membrane. Yet, although water quality may be good on the short term, one may rightly wonder what happens during aging of such membranes, especially when they are exposed to the sun's UV. To our knowledge, this has not been effectively researched. Consequently, it is best to closely monitor the emergence of odours. Fortunately, microfiltration systems that produce drinking water usually include an activated carbon filter that eliminates undesirable organic compounds if ever they crop up. For non-food uses, these compounds present no health risk, except for the unpleasant odour.
A flat roof consisting of exposed concrete is suitable as long as it is not used as a lounging area. Flat roofs that are covered with other materials are more challenging, as the choice of materials usually installed is predominated with tar- or asphalt-based membranes (see prior comments).
It is best to forget green roofs, very inefficient for domestic water reuse (and that's not forgetting the long term waterproofing problems, and the extra loads requiring an appropriate, more expensive structure). On the one hand, a green roof reclaims little water for the cistern, only during major rainfalls. In addition, the water will be loaded with impurities: humic particles giving the water a brownish colour, and lots of bacteria. The filtering system(s) will quickly be saturated, requiring frequent replacement of filtering components, mainly the 10-micron filter for non-food water production and the 5-micron primary filter on the microfiltration system.
We often forget that flat roofs, be they green or not, preclude any possibility of attic space in a house design, therefore eliminating any long term hope of refitting such a space for added bedroom space, as the family grows.
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.
Apparently, there exist many roofing products on the market where the primary material (or "substrate") is coated with a laminated synthetic compound during fabrication, e.g. pre-painted aluminium or pre-painted galvanized steel, imitation roof tiles with finish coats that aim to imitate traditional products, etc. The coatings can be rubberized spray-applied coatings, or synthetic enamels that are baked either chemically or with heat, etc. Some even integrate fine aggregates to give a texture to the product. There are many such products, each coming under their specific technology and manufacturing process. Unfortunately, we have no experience with the impact of these products on quality of rainwater running off their surfaces. There are generally no studies available on this. The question of aging of these coatings is also an issue. In doubt, for drinking water production, it is best to place an activated carbon filter upstream from the 5-micron filter. Moreover, when the primary roofing substrate is aluminium, it's best to periodically monitor rainwater quality in a cistern to check out the aluminium content with respect to standards.
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 on downspouts, 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.
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. They usually combine sediment filtration and leaf interception. Such filters usually come with a screening basket for easy maintenance, are relatively inexpensive and easy to use. These are very practical, but need to be inspected and 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.
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, better-designed first-flush water diversion systems are already available on the market, as seen on the Australian Rainharvesting web site.
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 7 500-litre (7 m2) 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. These cisterns are to be interconnected with piping at the top. Again, the sedimentation cistern's overflow will be a trapped overflow to prevent the transfer of floating impurities.
Try to avoid plastic and metal cisterns. To properly neutralize rainwater's natural acidity, prefer concrete, standard masonry or limestone.
Nevertheless, considering the fact that plastic cisterns (PVC, polyethylene, polypropylene) are less expensive and more easily transportable than prefabricated concrete cisterns, I recently conducted an experiment in order to see if rainwater could be stored in a plastic cistern, after it has passed through a small concrete cistern to neutralize it. The experiment was conclusive. Rainwater harvested from an 80-m2 roof was passed through a 1500-liter concrete sedimentation tank. This was sufficient to neutralize rainwater's natural acidity. From this tank's overflow, water can be conveyed to and stored in one or more plastic cisterns, placed underground.
You could even consider placing limestones or bags of limestone granules within plastic cisterns to neutralize the water. This last solution however makes maintenance a bit more difficult, i.e. to properly remove the sludge resulting from sedimentation when a cleaning is required.
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.
Many potential users want to know if any and all concrete is appropriate for rainwater storage planned for human consumption. What comes to mind concerns 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.
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.
To ensure good water conservation for whole-house reuse, a cistern must absolutely be put underground to minimize temperature fluctuations. 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 , but rather under a garage or a building annex for example. For an existing construction, it can be placed in the yard, under a pergola for example (the pergola being optional!). The cistern can be covered with decorative landscaping, plants, stone pavers, etc. Note however that grass planted above a cistern will yellow much quicker during dry spells. (Be reminded that the roofs of all annexes like the garage, greenhouse, garden canopy, firewood shelter, etc. should also be connected to the cistern to maximize water harvesting capacity.)
Placing a single prefabricated cistern requires large heavy machinery (truck, crane). For an existing home, limited space and access will sometimes make this option impossible. There are three alternate options:
Interconnected cisterns can more safely be linked together at the top, in the event of potential terrain or soil movement. Hence, the pipes interconnecting many cisterns must be flexible enough to absorb such movement. However, when you have more than one storage cistern, you need to adapt the configuration of your home's well pump set-up, as you may need to draw your water from more than one tank, meaning multiple piping and cistern equipment.
On the other hand, some propose interconnecting cisterns with piping located near their bottom. The advantage to this obvious: the cisterns become communicating vessels whereby their respective water levels automatically equalize. Thus, the well-pump dilemma is resolved. However, you become more vulnerable to water leakage that could happen surreptitiously at faulty pipe connections to the tank, or even total water loss resulting from a piping rupture in case of unexpected subsoil movement. In such events, repairs can be quite complicated, and expensive.
Finally, don't forget that the first tank (the sedimentation cistern) must have a trapped overflow to prevent the transfer of floating impurities to the storage cistern. The same type of overflow must be used between two or more storage cisterns, when piping is at the top.
When designing a system, one should also consider that a cistern also requires appropriate equipment for proper use and maintenance.
The inlet pipe to the home's pump system must have a one-inch minimum diameter. The pipe within the cistern must 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.
Include a tube feed to the bubble diffuser for the aquarium aerator or a pond aerator(available in garden and home renovation stores). It consists of a flexible plastic tube of less than 8 mm diameter. An aquarium or pond 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.
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.
Never connect the cistern overflow to a sewer. Laws in many countries, including Belgium, France and the UK 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  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.
Also consider ease of access and maintenance to the cistern.
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 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.
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. This remains preferable for smaller set-ups too, to avoid lighting your way down the cistern with a portable lamp, potentially dangerous when your feet are in water. You must therefore consider providing electric power to feed the lamp fixtures, but also the aquarium aerator. The control switches for these should be within the house and should come equipped with indicator lamps.
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. However, their electric consumption is much cheaper with bigger tanks, and the cost pay-back for a 200-litre tank is within a few short years. 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.
Note that we have had no experience with deep-well submersible pumps.
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.
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.
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.
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.
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 reduces the rainwater needs by 30 to 40%. This obviously only applies to those with a PLUVALOR system.
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 irrigation.
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 (often called a pneumatic gauge or vacuum gauge / vacuum manometer) 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 dubious 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, and the other at the cistern. It is a simple, practical and efficient solution. In fact, 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.
From a technical point of view, this is a rational approach, and is certainly very practical. But many 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 cistern's overflow level.
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.
Important : in all cases, make sure that the cistern water cannot get into the city water network. A proper check-valve placed after the water meter is mandatory. To avoid all risks, I recommend separating the city water fed plumbing circuit from the cistern fed circuit.
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