Is it legal to collect rainwater?
Yes, collecting rainwater is legal in France. However, this water is considered unfit for human consumption. It must come from precipitation collected downstream from a roof that is inaccessible to the public, except during maintenance operations. Its storage and use are permitted provided that the uses authorised by regulations are respected and that the rainwater system remains completely separate from the drinking water supply.
For simple outdoor use, such as watering the garden, a rainwater recovery tank connected to a downpipe is generally sufficient. As soon as the water is used to supply indoor equipment, the system becomes more technical. In particular, a separate pipe network, “non-potable water” signage and effective protection against any backflow into the public water supply must be provided.
- Rainwater must never be used for drinking.
- It must not be used for cooking, washing dishes or personal hygiene.
- Water outlets must be clearly identified.
- The rainwater system must never be directly connected to the drinking water supply.
- An installation with an indoor connection must be declared to the local town hall when it results in discharge into the public sewerage system.
Is it prohibited to store rainwater?
No, storing rainwater is not prohibited. An above-ground tank, underground tank or tank installed in an outbuilding may be used. The owner remains responsible for the safety of the system, its maintenance and the quality of the water supplied.
The tank must be closed and protected against the entry of leaves, animals and insects. In some municipalities or departments, local regulations require a cover and a mosquito-proof system. Checking with the local town hall will provide information about local requirements and any financial assistance available.
A tank that has previously contained a product of unknown origin or a chemical substance should not be used for sensitive applications. When collecting water intended for a vegetable garden, cleaning or an indoor system, a container with a known history that is compatible with the intended use should be selected.
What is the new decree on rainwater?
Decree No. 2024-796 of 12 July 2024, which came into force on 1 September 2024, updated the regulatory framework applicable to water unfit for human consumption. It defines rainwater as raw water collected downstream from surfaces inaccessible to people and specifies the permitted domestic uses.
In particular, the decree confirms that rainwater may be used for washing clothes, cleaning indoor floors, flushing toilets, decorative fountains not intended for consumption, cleaning outdoor surfaces, washing a vehicle at home, watering vegetable gardens and watering green spaces at building level.
These permitted uses do not remove the applicable health requirements. Installations must prevent any risk of contamination of the drinking water supply. Washing clothes with raw water is also subject to a declaration procedure with the prefect before the system is first put into service. For a system connected inside a home and discharging into the sewerage network, a declaration to the local town hall is still required.
The regulatory framework also includes the Order of 12 July 2024 concerning the sanitary conditions for the use of water unfit for human consumption. For an indoor, shared or public-access project, it is advisable to have the design approved by a professional familiar with these regulations.
How can homeowners reuse rainwater?
Watering the garden and vegetable garden
Watering is the simplest use. Rainwater can supply a watering can, hose or drip irrigation system. Upstream filtration helps reduce leaves and deposits. An opaque tank or one protected from light helps reduce algae growth.
Supplying toilets
Collected water can be used to flush toilets via an independent system that is clearly identified and kept separate from the drinking water supply. A pump, suitable filtration, signage and a backflow prevention device are required. The installation must be capable of being shut down quickly in the event of a malfunction.
Cleaning floors, washing clothes and outdoor cleaning
Cleaning indoor floors and washing clothes are permitted under the regulatory framework, with stricter requirements than those applicable to watering. Washing clothes requires a declaration to the prefect. Outdoors, rainwater can be used to clean tools, patios and vehicles at home.
What water quality can you expect?
Rainwater is not drinking water. As it runs over the roof and through the gutter, it can pick up dust, bird droppings, pollen, microorganisms, metals or residues from roofing materials. Water that looks clear to the naked eye is therefore not necessarily suitable for every use.
Water quality depends on four main factors.
- The collection surface and its condition.
- The presence of a leaf guard and an accessible filter.
- The opacity, closure and cleanliness of the tank.
- The storage period and water temperature.
For sensitive or professional applications, water analysis may be necessary. No standard treatment automatically turns a rainwater tank into a supply of drinking water.
What solution is suitable for farmers or professionals?
The large roof areas of agricultural and industrial buildings make it possible to collect significant volumes of water quickly. One millimetre of rainfall on one square metre of roof theoretically represents one litre of water before losses due to the roofing material, filtration and overflow are taken into account. With a 500 m² roof and 10 mm of rainfall, the gross collection potential is therefore 5,000 litres.
Several 1,000-litre tanks can be connected to create a modular water reserve. This solution is suitable for cleaning outdoor surfaces, watering green spaces and certain technical requirements. Sizing must take into account gutter flow rates, actual consumption, available space, frost and the frequency of dry periods.
For crop irrigation, watering livestock, cleaning equipment that comes into contact with food, or use within a food business, the rules vary depending on the activity and level of risk. Before carrying out any work, the intended use should be defined with the Chamber of Agriculture, the relevant government authorities or an engineering consultancy. Water analysis and monitoring procedures may be required.
A professional installation should also provide easy access to filters, sufficient overflow capacity, isolation valves and a maintenance plan. Adding multiple tanks without assessing the incoming flow rate may simply shift the problem to the gutters or the areas surrounding the building.
Why choose a 1,000-litre tank?
The 1,000-litre IBC format offers a good balance between capacity, footprint and budget. Its standard dimensions of approximately 100 × 120 cm make it easy to install along a wall or under a lean-to. It can also be connected to a second tank when requirements increase.
The choice of a 1,000-litre rainwater tank should be based on the intended use, the container’s history, the opacity of the inner bottle, the type of pallet and the condition of the valve. An opaque inner bottle is particularly useful when the tank remains exposed to light.
To estimate the volume of water that can be collected, use this simple formula.
Annual volume in litres = annual rainfall in mm × roof area in m² × collection coefficient.
The coefficient takes into account the roofing material and filtration losses. It is often between 0.5 and 0.9. A 1,000-litre tank can therefore fill very quickly during a period of rainfall. Its capacity should be compared with water requirements between rainfall events, rather than solely with the theoretical annual volume.
Above-ground, underground or flexible tank: which should you choose?
| Type | Advantages | Points to consider | Recommended use |
|---|---|---|---|
| Above-ground tank | Simple installation, controlled cost, easy access | Light exposure, frost, visual integration, stability of the base | Garden, vegetable garden, outdoor cleaning |
| Underground tank | Large capacity, space saving, water better protected from heat | Excavation, accessibility, groundwater, vehicle loads, cost | Homes, shared buildings, regular requirements |
| Flexible tank | Quick installation, large capacity, can be installed in a crawl space or agricultural building | Base must be perfectly prepared, protection against punctures | Agriculture, commercial buildings, seasonal storage |
What budget should you allow for rainwater collection?
The budget below is calculated using the prices displayed on the Containers Service website at the time of writing. Prices are shown excluding VAT. Stock availability, prices and transport costs may change.
Example budget for a simple 1,000-litre installation: a reuse tank at €95.00 excl. VAT, a gutter connection kit with filter at €14.70 excl. VAT and an outlet with tap at €26.30 excl. VAT give a total of €136.00 excl. VAT, excluding delivery, base preparation and overflow components.
Example with a tank fitted with a new inner bottle: the tank at €216.00 excl. VAT, the gutter connection kit at €14.70 excl. VAT and the outlet with tap at €26.30 excl. VAT give a total of €257.00 excl. VAT, excluding delivery, base preparation and overflow components.
Example for 2,000 litres: two reuse tanks at €99.00 excl. VAT each, a gutter connection kit at €14.70 excl. VAT, a two-tank connection kit at €41.51 excl. VAT and an outlet with tap at €26.30 excl. VAT give a total of €280.51 excl. VAT, excluding delivery, base preparation and overflow components.
These examples use only products available from Containers Service. Before ordering, check thread compatibility, the exact contents of each kit and product availability. A pump, indoor pipework, excavation for an underground tank and labour should be quoted separately.
Some local authorities provide grants or distribute rainwater collectors. The local town hall or intermunicipal authority can provide information about available local assistance, eligible capacities and the supporting documents required.
Where should the overflow from a rainwater collector go?
The overflow must safely discharge the entire incoming flow when the tank is full. Depending on local regulations and soil conditions, it can be directed to an infiltration area, swale, rain garden, dedicated stormwater system or a second tank.
Connection to the public stormwater network is only possible if permitted by local regulations. The overflow should not be discharged into the wastewater network without authorisation. When the overflow is connected to a pipe, a non-return valve and protection against insects and small animals entering the system are recommended.
The outlet must be sized to handle the maximum flow rate from the downpipe. A small opening or a kinked pipe can cause the tank to overflow near the foundations.
How do you install a rainwater recovery tank?
A 1,000-litre above-ground tank weighs approximately one tonne when full. It must stand on a flat, stable, load-bearing base free from sharp or uneven surfaces. The collection system should include, at a minimum, a leaf guard, an accessible filter, a water inlet, an overflow and a draw-off point.
An indoor installation also requires a pump, a separate pipe network, backflow protection from the drinking water supply, signage and sometimes a mains water backup system. The choice of tank accessories depends on the valve thread, the diameter of the downpipe and the required flow rate.
Read next: our dedicated guide to installing a rainwater collector will explain base preparation, connection to the gutter and overflow adjustment in detail.
How do you maintain and winterise a rainwater collector?
An annual visual inspection is the minimum recommended maintenance. Check the condition of the tank, watertightness, lid closure, filter cleanliness, valve operation and proper overflow drainage. Clean the gutters and remove deposits from the bottom of the tank according to the condition of the installation and the manufacturer’s recommendations.
Before freezing conditions occur, shut off the water inlet, drain exposed pipes and protect the valve. An above-ground tank exposed to severe frost may need to be emptied. Never add antifreeze to the stored water.
Read next: our guide to cleaning and winterising a tank will explain how to drain the tank, clean its walls and put it back into service.
Economic and environmental benefits
Collecting rainwater reduces the use of drinking water for purposes that do not require potable water quality. The financial savings depend on the local price of water, the volume actually used and the cost of the installation. A simple system dedicated to garden watering will generally pay for itself faster than a complete indoor network.
The environmental benefit is not limited to lower water bills. Temporary storage also reduces some runoff during normal rainfall, provided that sufficient capacity remains available in the tank. The reuse of a suitable container can also reduce the need for new materials. These benefits depend on a correctly sized, properly maintained installation that is used regularly.
Frequently asked questions about rainwater collection
Can you drink water from a rainwater collector?
No. Rainwater collected from a roof is not drinking water. It must not be used for drinking, cooking, washing dishes or personal hygiene.
Can rainwater be used to water a vegetable garden?
Yes. Watering vegetable gardens is one of the permitted uses. It is still advisable to filter the water, keep the tank closed and avoid using a container if its previous contents are unknown.
Do you need to declare a 1,000-litre tank?
A tank used exclusively outdoors, with no indoor connection, is generally not subject to the declaration requirements applicable to indoor systems. A declaration to the local town hall is required when an indoor connection results in this water being discharged into the public sewerage system. Washing clothes with raw water is also subject to a declaration to the prefect.
How long can rainwater be stored?
There is no single storage period applicable to every installation. Water quality depends on the roof, filtration, tank opacity, temperature and maintenance. Water with an unusual smell, abnormal colour or significant visible contamination should not be used without further checks.
