Abstract: A method is provided for purifying raw water taken from a raw water reservoir. The method includes the steps of subjecting the raw water to magnetic treatment, causing the magnetically treated water to flow through a filter medium in a first direction for purification of the treated water, and discharging the purified water into the raw water reservoir. The method further includes the steps of causing the magnetically treated water to pass through the filter medium in a second direction opposite to the first direction, and discharging the oppositely passing water into the raw water reservoir. The apparatus for realizing the above method includes a water intake assembly, a filter assembly and a water discharge assembly. A magnetic treatment device is mounted on the water intake assembly for subjecting the raw water to magnetic treatment. A switching device is operated to cause the magnetically treated water to flow through the filter assembly selectively in the first and second directions.