There is a reason people say look at your maps and it's not just for water sources. It's to make sure you have a safe trip, especially if this is your first season hiking.
I don't like the Harrison Maps. The map Doug has at the store is ideal for the novice taking this trip. It is 1:24,000, compact with shaded relief. However, if you want something now pick up the Mts. Langley and Whitney USGS Quads. Most of the people I have helped getting "found" in the mountains seemed to be utilizing Harrison Maps, this could be just my experience.
The water sources you need to know about are at Trailside Meadow and Trail Camp.