Tony, since this is an out and back hike, I would suggest you do it this way. Start your hike with an extra quart or two of water (carried by you, the young buck). Carry it in and stash it in the woods slightly off the trail near the bottom of the big hill, which is on the fire road just north of the Cascade Creek bridge. Then attempt to pick up some cool water from Cascade Creek if any is present. On the way back to the car later in the day, you pick up cool water from the creek again, or else you have the stashed water as a backup. The two uphill places along this trail are where you will need the water the most. One is at about Mile 4-5 on the way going, and the other is over the last 2.5 miles heading home. The former is worse since it is sun-exposed, but it would be earlier in the day, so it won't be so hot. The latter will be late in the day, and you will be too tired to do anything more intelligent with water.
The Yosemite Backcountry Office is notorious for being poorly informed on specific trail conditions. They get some trail reports early in the season when they are trying to get trails open. But late in the season, they figure "who cares?"