WordNet sense 1 (a viscous glass consisting of sodium silicate in solution; used as a cement or as a protective coating and to preserve eggs):

soluble glass, sodium silicate

WordNet sense 2 (gauge for indicating the level of water in e.g. a tank or boiler or reservoir):

water gauge, water gage

WordNet sense 3 (clock that measures time by the escape of water):

clepsydra, water clock