I noticed the thread moved from the original arsenic issue. That is a huge disaster that is building up like a timebomb. I work with a human rights group that sponsored a pond last year as part of a groundwater reservoir cleanup program. It's an alternative to some of the higher-tech filtration options and seems to work, but the jury is still out somewhat as to what would really be cost effective and implementable.
If you are interested there are some great reference links on the problem and what is being done at the following Drishtipat campaign page:
http://www.drishtipat.org/past/arsenic/index.html