If it's a large named feature on a map (like the San Joaquin River or Garnet Lake), it will reliably have water.
Even lots of the smaller unnamed springs, ponds, creeklets, etc will have water most years, but as others have pointed out, more of these smaller features could run dry as we get later into this exceptionally dry year.
Generally, I don't worry much about being able to find water in the Sierra. Just consult your map throughout your hike. If you see you're coming up on a long, dry ascent over a pass that doesn't have any creeks intersecting it or easily accessible tarns along the way, then stop and tank up.