Thanks for your compliments 9anda1f, There are no hard and fast rules with these pools. Designs can vary wildly. Water quality is the most important goal in my opinion and this will also vary wildly depending on construction and location. Drinking quality water is a reality from a well designed system, and is the benchmark that I must aim for when building for other people. Many of the pools that I have seen on the net don't appear to have the ability to be cleaned / vacuumed. Being able to vacuum a natural pool is a must, but it takes something very different to a conventional pool filter or cartridge filter. Algae is the main concern that I have noted from around the world. Algae is not so much the problem, rather the inability to remove it easily without wasting large amounts of water. When I vac my pool, I use about 60 litres of water to clean my mechanical filter. No other water is ever lost from the system other than from evaporation. My pool water ph is 7.5 constantly. Hardness is 17 mg/l CaCo3. Funny how it is called hardness, my water is very soft. Turbidity is 0.5 NTU, very clear. Ecoli when tested in mid summer was 3 organisms per 100 ml.