I have "inherited" a house with a water system that is cleaned through a concrete-housed sand filter. There is only a small layer of sand left and dirty throughout...so, I guess its time to start afresh... The concrete ring is 0.8m in diameter and 0.8m high, with water piped into two concrete tanks. It looks like the old "sand" also had what looks like rice husks in it and may be a specialized mixture? I am wondering if anyone can advise me where I can buy the right sized quality sand or any specific mixture for sand filters and how thick the layers of sand and rocks should be? Can I re-use the bottom layer of rocks, or do they just need to be hosed down? Thanks!

Here's another discussion on this topic with some links that may help. http://www.thaivisa.com/forum/topic/88935-thailand-slow-sand-water-filter/