Just back from 2-day hike. Ran out of water fairly quickly (had 500ml on my side and 2L in my pack). I live in Scotland so mountain streams are fairly easy to come by and are probably the best possible water you can get, however the only thing i know is not to get water from near the trail or from lochs. What if i have water treating tablets? How far can i stretch water filter techniques? Is there a rule of thumb other than 'fast and downhill'?

also, Share your water-related stories, tips, as staying hydrated is one of the most essential parts of any trip.