There are a lot of bison in Theodore Roosevelt National Park, but that's not why I uploaded this picture.
The NPS says there is no potable water in TRNP. The staff I talked to were not very helpful about why the water isn't potable. But look at Paddock Creek on the left-hand side of this picture. Most of the creek was dry when we were there, only one day after a series of rainstorms in mid-May 2010. When there were pools of water, the good ones looked like this.
A gallon of water a day per person weighs just under nine pounds. Happy backpacking!