3P Technik Filtersysteme GmbH

How does rainwater harvesting work?


1) Collecting rainwater:

Water is collected from sealed areas, normally roofs.
How many water is available at an average?
Quantity of precipitation l/m² x roof area A m² x discharge coefficient 0,75 = available quantity of water

E X A M P E L: 700 l/m² x 120 m² x 0,9 = 75.600 l/year


2) Filtering rainwater:

Rainwater normally has the quality of bath water if it is cleaned through pre-filters. Finely woven and self-cleaning filters made of stainless steel with a high efficiency are especially suitable for this.


3) Storing rainwater:

Most suitable is the installation of an underground tank thus avoiding germ formation (no light, no heat). Concrete cisterns additionally have a neutralising effect on the rainwater.

How big must the cistern be?

Number of persons in the house x per capita consumption in liters plus part of the garden x security stock 21 days = size in m

E X A M P L E: (4 persons with 400 m² garden) 4 persons x 69 l x 21 = 5.796 l

For this example we would recommend a cistern of 5 or 6 m. One rule of thumb out of experience: per m capacity you need aprox. 25 m² roof area.


4) Removing rainwater:

The water is removed by submersible pumps. As soon as water is being removed, a presscontrol is activating the pump and also stops it afterwards. Submersible pumps have the advantage that they work silently and are providing a constant pressure when watering the garden.


5) Topping up rainwater:

If it does not rain and the toilet flushing has to work anyway. As the circuits for the rainwater must not be linked to the normal circuits of potable water (DIN 1988), potable water is led into the cistern. Of course only in small quantities which cover the daily demand.

Wie funktioniert Regenwassernutzung

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