Drinking water was any fresh water or ground water supply that was deemed as clean water, suitable for consumption (i.e. free from contaminants). Starfleet ration packs included individual water packs or water rations.
As of 2151, the water supply of the Novans at the northern hemisphere on Terra Nova were contaminated by toxic debris from an asteroid impact almost seventy years ago. They agreed to be relocated to the southern hemisphere. (ENT: "Terra Nova")
In 2153, MACO soldier F. Hawkins offered T'Pol some water from a canteen aboard the D'kyr-type starship Seleya. (ENT: "Impulse")
In 2372, when marooned on Hanon IV, Kathryn Janeway declared finding drinking water to be the most important task, followed by finding shelter. (VOY: "Basics, Part I")
Water was a standard part of all Starfleet emergency rations packs. In 2367, Captain Jean-Luc Picard and Ensign Wesley Crusher were stranded without water after crash landing on Lambda Paz, a desert-like moon of Pentarus V, since their shuttle pilot Dirgo never found time to pack water in the emergency supplies. (TNG: "Final Mission")