I saw this on TV a while back and have been keeping an eye on prices. It seems it will clean Chiang Mai Moat water into drinking water. 4000 litres or 6000 litres depending on model. If you buy lots of bottled water this could be worthwhile. Less than 3Baht a litre.
http://www.lifesaversystems.com/index.html
http://www.lifesaversystems.com/index.html