Locally backwashing portions of filter media allows a simple and effective design of intake and pretreatment units, as well as their integration. An enclosure is used to limit portions of filter media and backwash them locally by suction, utilizing filtered water from adjacent filter media as the back wash water. Wastewater is produced at small amounts that allows efficient sludge treatment. This design enables water pretreatment at the intake unit, simplifying overall plant design and preventing damage to organisms living outside the intake unit.

A backwashing apparatus 110 for a filtering system comprises and enclosure 119 having an open lower end, positionable above a surface of filter media 92 supported by a drainage area 96. A pneumatic system such as an air pump, is in fluid communication with the upper part 127 of the enclosure and is configured to determine an air pressure therein. A pipe system connects the upper part of the enclosure with the pneumatic system and with a discharge structure 132. A control unit is connected to the pneumatic system. The enclosure is provided with a water inlet 120 for selective delivery of water from outside the enclosure to within the enclosure during sinking of the enclosure into filter media. Also disclosed is a method of backwashing a filtering system. The backwashing apparatus may be used to pre-treat water.