We use a tiny Katadyn 40e - only about 5litres an hour but can just about run it from one of our solar panels (via a battery) We fill a 15l gerry can each day over a few hours and that usually is about enough for us - although we are dirty and smelly cruisers. Don't misunderstand me, we would love a 20 or 50 l/hour monster but we dont usually use that much water daily and dont have the power/space/dosh etc. What it does mean though is it gets a fair bit of excercise. Personally, and I'll temper that with the fact that I'm often wrong, a small one that you can run often is possibly better than a large one run infrequently. Unless anyone fancies giving me a bigger one.....I promise we will wash more.