The Who's Pete Townshend Drinks Pedialyte Onstage

The Who kicked off the final night of the "Oldchella" (aka Desert Trip) music festival Sunday night, and the rock legends were prepared ... for dehydration.

While 71-year-old Pete Townshend jammed on a guitar solo, he kept a bottle of Pedialyte nearby. It's important to keep up on your fluids in the desert, especially for seniors.