There was water at LRV when I was there on July 6 as well as when I was there on Sept 7. In Sept, it was raining, so I'm not sure how much of an indicator that is. Do take a look at
Water Sources of the San Jacinto Mountains. There's a specific spot in LRV that is most likely to have water (if water is hard to find).
If there's no water at LRV, then there almost certainly will be water at Lilly Spring which is something like 0.3 miles back down the trail. The water flows right across the trail, so it's not hard to find.
If for some reason Lilly Spring were out of water, you could go to Bed Springs. You could go cross country and hope to find it (not hard if you're used to cross country nav) or you could go back down the trail past Lilly Springs to where the water from Bed Springs crosses the trail (what I call Bed Springs Crossing). This is an
easy to find, reliable water point. It's about 0.5 miles from LRV, but it beats carrying it in from the trailhead.
HJ