And Outpost is still high enough to make a difference. I wholeheartedly second the recommendation to sleep there.
Lots of very sound advice here, and none that I would second guess.
I overnighted at Onion Valley in early July and it was dry--no water supply at all, and all of the faucets were off. Based on the age of the signs, it was not a recent development. There are streams that you can reach, or just grab a whatever jugs you need in LP before heading up like I did.
Have fun!
