Many old farm buildings still have tanks to take the run-off from roofs. Examples range from stone and cement structures built on to barn walls to well-like structures, both fed by gutters from the roof.
Installing rainwater systems means you can water your garden without worrying about bills – and you can water when restrictions are in place.
If rainwater is used in the house, water consumption can be halved, although the relatively high cost of installing systems means it will be years before financial benefit is felt through lower bills.
It is also possible to build your own buried tank relatively easily, especially if you have access to a mechanical digger for the hole. A great variety of rainwater tanks, mainly plastic, can be bought at garden shops.
Regulations for rainwater use are strict – it must not be used as drinking water, for cooking, or for baths or showers.
This is because, contrary to popular belief, it is not pure and usually contains measurable traces of pesticides, dust, soot and other chemicals. They are taken up by water molecules in the atmosphere and end up in rain.
If your roof contains lead, as many grey zinc roofs in cities do, or it is made of asbestos-cement, rainwater gathered from it is banned for use inside houses. It can still be used for the garden and washing cars.
Water from other roofs can be used for toilets, cleaning floors and clothes washing, although for clothes it should be filtered and treated against bacteria.
Rainwater is very soft, so it is good for washing machines, and can be used to fill swimming pools.
If your property has a septic tank, the rules are simpler than where you are connected to the local sewerage system.
In either case, rainwater must only be collected from the roof of buildings, rainwater tanks can either be buried or above ground, and you should not use anti-freeze in the tank.
Any interior taps for rainwater must have a label stating eau non potable (not drinking water) and the same label must be attached to pipes carrying rainwater to a lavatory.
Rainwater taps are banned from rooms where there are drinking water taps, except for cellars or annexes, such as laundry rooms and garages.
There must also be a shut-off valve for the rainwater system, which should be activated only with a special tool.
Rainwater systems indoors must be maintained every six months, by the home-owner or a plumber, and details logged in a notebook. This includes checking the system is clean, labels are present, and there are no connections between the rainwater and drinking water systems.
Once a year, all filters should be washed, the rainwater tank should be emptied, cleaned and disinfected, and all the valves tested to make sure they work.
If you rent out the property, you should explain to tenants how the rainwater system works, and if you sell it, you have to tell the buyer about the system.
For those on a collective sewerage system, the installation of a rainwater tank must be accompanied by a declaration at the mairie, where it will be sent on to the water authorities, usually now linked to an intercommunal body.
The declaration, written on blank paper, has to give the address where the tank is installed, and an estimate of the volume of water from all sources used inside the house. It will be used to determine the taxes due for wastewater treatment.
If the water authorities decide they need to inspect the system, you can be billed for this.
You will be obliged to follow any recommendations if the water authorities think your system might contaminate the drinking water system.
If you decide to have professionals install a rainwater system, the bad news is that a 30% tax credit which used to be available was removed in 2019.
The good news is that TVA/ VAT is limited to 10% if the work is done by a professional with RGE status (Reconnu Garant de l’Environnement).
Some departmental councils have grants towards installing rainwater systems, so it is worth asking if this applies.
To check if ordinary water restrictions apply in your area, click on the map at tinyurl.com/dxe62k3.
More on this topic: Tips for buying a rainwater tank in France
