Excellent point. I would look into staying a few days at Tuolumne, rather than in the Valley, to prepare and acclimatize. Its at about 8500 feet as opposed to 4000 in the Valley. Lots of higher day hikes from there. And if you want to really blitz that first 20 or so, you can leave all but essentials at Tuolumne, pick it up on on way back through. If you want to resupply, look at Muir Trail Ranch. Its about half way, adds little if any distance just a little up and down, unless you are a purist; quickest stop there does bypass a couple miles of the JMT.
This year, even in August, your only water (quantity) issue should be in the Whitney Zone, where you can expect to go from about Guitar Lake to trail Camp without a refill. That's about a 3 quart jaunt. Check Wenk for this, but I would be surprised if you need to carry more than a quart anywhere else. Water quality is another thing to look carefully at. More and more people are dipping and sipping, some still using filters, UV and/ or iodine.
