Explication filtering diagram

 The polluted water is pumped into the filtration system (6); a flocculation unit (7) makes possible the agglomeration of the impurities and their transfer into the decantation tank (8). Filtration is carried out by the filter (1), water passing through several layers of sand of different granulometry (sizes). When the water comes out of the filter it is clear and it is further sterilized by ultraviolet means to makes it drinkable (20.000litres/24 hours) Water for everyday use is directed to the main tank (4), whereas a part of it is stored in an extra (spare) tank (3) for later filter washing. After some period of use, the filtering components become clogged up. By means of two valves one can reverse the flow of stored water (3) across the sand layers and wash them. This dirty water is evacuated and as soon as this operation has been carried out, the water flow is redirected to its original direction by means of the two valves. A built-in chlorination unit (5) is designed to substitute for the U.V. device in case the latter fails. When washing the filtering mass (5) this unit can be used or by-passed. Tests have been carried out in specially difficult conditions with the water of a river where the concentration of silt and sand varied to an important degree. Inspections have confirmed that the quality of the filtered water meets with Swiss standards.