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Rainwater harvesting

Rainwater can be used for certain tasks that do not require drinking water; this is the case for our laundry, toilets, showers or even for watering our surroundings. However, each country has its own legal framework and the possibilities could change from one country to another.

A few figures

With a 100 m² roof, it is possible to recover between 3000 and 6000L of water. This depends of course on the rainfall rate of each region.

How it works

Generally speaking, rainwater slides from the roof to the gutters, which are connected to a tank in concrete or HDPE. Water enters the tank after passing through a filter. The distribution can be done by taps and in this case the tank is above ground. But it can also be done by pumping and the tank is then buried.


The regulatory framework

Regulations are very strict on this subject. In France, for example, rainwater harvesting for the house is not allowed for consumption and is prohibited for showers and dishwashers.

In Portugal, water network and rainwater use cannot be mixed. The two systems must be independent. It is essential to know from the design stage of the project about the regulations in force in each country and to adapt its rainwater harvesting system accordingly.

This discharge of rainwater leads to a discharge of water into the sewerage system, and anyone connected to the sewerage system who is supplied with water must pay a fee. Rainwater that is discharged into the network is also subject to this tax. It will be calculated by means of metering devices or on the basis of criteria to estimate the volume of water discharged.

Many advantages…

In addition to the obvious financial and environmental benefits, this technique also benefits pipes and taps since they are much softer than spring water and therefore protect household equipment from scale.

It is not advisable to have a wooden roof or a green roof, as this may hinder the recovery of rain.