The filter's functional concept is based on transporting the contaminated water through the layer of calibrated sand. The contaminants will be trapped on the surface of the sand, and the treated water will come to the final filtration. When the filter is clogged, it has to be washed by the reversed water flow. Filter sections will be washed in turn. During that, every new section will be washed by water that has already been filtered by the previous sections. Each section can function individually or simultaneously with others, so the filter washing mode may be active during irrigating.