The Los Angels River is many things to many people and on one recent Saturday evening, for Ashley Sparks, it was art. She was one of a few dozen people who sat down at the river’s edge for the opening of an art activation called “What Water Wants” by Roston Woo. … “What Water Wants,” part of PST ART: Art & Science Collide, is a half hour audio presentation that involves music, ambient sounds and narration — a kind of guided meditation that is available on your phone at any time through a QR code posted near Lewis MacAdams Riverfront Park.