 The general rule of thumb is to carry a half a liter of water for every hour you plan to be hiking. So after all that hydrating, what if your miles from a restroom went on the trail? She says do what you have to, but leave no trace. If you're using toilet paper or something similar, put it back in your backpack, put it in your pocket, walk it out to the trailhead, put it in a garbage can, or take it to your car and bring it home to throw it away if there's no garbage can available. Kate Ryan, WTOP News.