Me and water... here's the story...
There was a time when I used to bust my guts on the hills, rushing up and down everything in sight, and I would drink water like it was going out of fashion. Any water, anywhere... within reason. I've never had any problem with water that runs off hillsides, no matter how many animals might be peeing and pooing in it. I draw the line once water has passed through a farmyard or other habitation. Whether or not this is a 'sensible' approach really doesn't bother me. I make up my own mind whether or not to drink from a source, and so far, they've always been good.
As for carrying water... I avoid it at all costs when I know I can get it more or less on demand off a hillside. Now, bearing in mind that in recent years it's been my lot to explore and write about a lot of hot, dry places... Canaries... Mediterranean... I tend to take a different approach. If I'm in a hot, dry place for a month, I'll usually carry 2L of ordinary tap water for a day's walk at the start, but within a couple of days I'll adapt and drop the amount I carry to 1L. By the end of a week, it's quite usual that I won't bother carrying or drinking water all day long. In hot places, I don't bust my guts, rarely work up a sweat, and just plod along slow and steady. My only concern is if I'm planning an overnight camp, for which I'd probably want 4L of water for food and drinks, covering evening meal and breakfast. With 4L in me, the next day will be fine and I won't need to carry any water. Even in hot, dry places, I can usually find water at least once a day.