Subclass 3/26: Methods or installations for obtaining or collecting drinking water or tap water (treatment of water C02F) from underground Obtaining and confining water by means of wells (applicable to a combination of water and other liquids or to other liquids only E21B 43/00) Component parts of wells Well filters (filters in general B01D 24/00-B01D 35/00) formed of loose materials, e.g. gravel with packed filtering material