Thanks! After a bit of searching, it appears that it should be a https://wiki.openstreetmap.org/wiki/Tag:man_made%3Dwater_tap + https://wiki.openstreetmap.org/wiki/Key:drinking_water either no or conditional + either untreated or boil? Is the tank signed at all? & if you're feeling enthusiastic, you could also map teh tank itself: https://wiki.openstreetmap.org/wiki/Tag:man_made%3Dstorage_tank + content=rainwater (which I've just created! :-)) Have fun! :-)