Here are some links that explain different ways to remove Arsenic from Ar-contaminated water.
- Removing arsenic using PVA bottles.
- Arsenic removal using water hyacinths.
- Improving Water quality in India.
- Safe Water Technology for Arsenic Removal.
- Groundwater Arsenic Contamination in India: Vulnerability and Scope for Remedy
- Using cysteine as an Arsenic magnet – Earthsky; Homeland Security;
- Arsenic conversion from As3 to As5 (What can I do if my water has high arsenic levels? second paragraph)
biodesign for the real world 
There is a chapter in this book about waste water treatment –
http://books.google.ch/books?id=hMA70VU36qUC&pg=PA223&lpg=PA223&dq=arsenic+environmental+switzerland&source=bl&ots=AM7gvooe1V&sig=YzjcA1Sv41dxcLXmLCGm97okQwI&hl=en&sa=X&ei=n596UdHYFsaXPe25gbAN&redir_esc=y#v=onepage&q=arsenic%20environmental%20switzerland&f=false