water would have to be terrible not to swim in, so you'll be fine there. for drinking, especially since the DWG is at lower elevation, i wouldn't recommend drinking unfiltered water.
if you're hiking and want to drink unfiltered water, then generally only do so if you're getting the water directly as it's coming out of the ground, since the ground has a way of filtering water. but generally speaking, don't drink water untreated. you're unlikely to get anything bad as far as chemicals go, but you leave yourself open to stomach viruses that can make you sick for a while.