I watched a news previously and did some research on invest in companies that sanitized Water. The article can be read at SeekingAlpha.
I personally like PHO (US) - POWERSHARES WATER RES PTF. It pays a dividend of 14 cents per year. I personally do not own any of the Water ETF (enclosure). Take a look at these Water ETFs. The author states that Water ETF is a great long term hold in the next few decades.