Drips to oceans
Water is one of the most versatile sound sources. Close up, drips and bubbles are pitched and percussive; a little further away, pouring and splashing work as foley; at a distance, streams and waves become ambience. Producers use water for texture under ambient tracks, sound designers for scenes and games, and many people for relaxation.
Choosing a recording
For foley, pick dry, close recordings with one clear action. For ambience, look for long, steady recordings without voices or traffic. Waves and rivers contain a lot of low end that can muddy a mix, so a high-pass around 80 to 150 Hz is common.
Nature recordists share a lot of water on Freesound, Wikimedia Commons and the BBC Sound Effects archive. The BBC recordings are for personal, educational and research use only, so they carry a red verdict for releases; the others say on each card what you may do.