Detecting and Reducing Arsenic Contamination of Groundwater

Arsenic contamination of groundwater is a form of groundwater pollution which is often due to naturally occurring high concentrations of arsenic in deeper levels of groundwater, which creates long-term exposure of people to arsenic.

From a 1988 study in China, the US protection agency quantified the lifetime exposure of arsenic in drinking water at concentrations of 0.0017 mg/L, 0.00017 mg/L, and 0.000017 mg/L are associated with a lifetime skin cancer risk of 1 in 10,000, 1 in 100,000, and 1 in 1,000,000 respectively. The World Health Organization asserts that a level of 0.01 mg/L poses a risk of 6 in 10000 chance of lifetime skin cancer risk and contends that this level of risk is acceptable. (wikipedia)

Any ideas on cheap methods of reducing the levels of arsenic in potable water and soil in the affected territories in India, Bangladesh, Argentina, China, Nepal and other places of the world would be highly desired.