1) Precaution for drinking 2) Remover of impurities 
A water filter removes impurities from water by means of a fine physical barrier, a chemical process or a biological process. Filters cleanse water to different extents for purposes like irrigation, drinking water, aquariums, ponds and swimming pools. ==History== During the 19th and 20th centuries, water filters for domestic water production were ...
[n] - a filter to remove impurities from the water supply
noun a filter to remove impurities from the water supply