We are planning a extended trip to Big Ben National Park in March 2014. I received a note from a friend who just came from there. They said "The resorts at Big Bend National Park have their own water ...
Much of the water at Big Bend has relatively high mineral content. The only area of the park where I'd consider it a problem is at the Cottonwood Campground at Castolon on the west side of the park. The park provides drinking/cooking water in the campground via a reverse osmosis system. Other water supplies there can be used for cleaning but is not approved for consuming.