I got asked a question about what I do for water at high wild camps where there is often no water? The answer is very simple. But there are a few points to take into consideration.
I will use a wild camp I did in the Lake District as an example. I had walked with Mike Knipe and as we went our separate ways he had commented about water for my wild camp on Great Borne. My response was that I planned to check out the stream source on my map before striking out for the top, and to carry 2L up from that point with me for the night and morning. It had not been an extended dry period and I was anticipating finding water.
When I am wild camping high the most important thing is the weather forecast and anticipated wind speed. I want to ensure the wind won't flatten my tent or shelter. If the weather is worse than forecast I want to be somewhere that I can bail out from fast and easy. No rocky ridges to follow on the way down - or boulder fields. Easy slope down and to shelter.
Once I have that, water is the least of my worries. That I will get on the way up. Finding a high stream outside of summer is not hard. Warm dry periods would find me carrying water for the camp from lower down. Not worth the risk of finding a dried up stream high up. High streams often dry up in prolonged dry periods.
High streams are for the most part clean water. If it's clear and running, has no cattle herded above the water source, or other likely sources of contamination I would drink from it there and then. Have a good litre to help hydrate - then fill up my water bladder for camp. When you find the source of those high streams the water you know has no dead sheep in it or anything to worry you (tip: use a buff over the opening of your water bottle to filter anything out if you think there are contaminants, then drop a water purification tablet in, or use a filter if you carry one)
If it's clean and running have a tipple. If it's still and dark give it a miss. The water for the wild camp I mentioned was found just off the path, clear from the point it was springing up out of the ground. When it's like this you can't go wrong. Fill and hold the container up in the light. Clear, no coloration or floating bits is what you want.
So let's get technical. A litre of water is 1000g/2.2pounds. You fill up your 2L water holder for that high camp where there is a water source. You might want to carry that 4.4pounds extra for the least distance possible. So study maps and suss out where the last clean water source will be.
I don't get water from high tarns, by the way. Still water is a concern for me. Some do. I don't. It needs to have had some movement for me. Finding streams high up I find not hard. The skill is judging when to fill up.
If I need to get water lower down I treat it, and have a good hydration session there once the treatment has done its task, then head up lugging water for the wild camp.
Getting water for a high camp is very easy once you get into the habit of finding springs and stream source points high up. Check maps and enjoy the views high up. Also, don't forget: snow is wonderful. You can melt it for water. Always nice to find a remaining drift of snow high up. Melt the water and bring it to a boil. Job done.