In this area, the aquifer groundwater is contaminated by As (average 121 μgL−1
340 μgL−1)(Berg et al., 2008) and in most cases the groundwater and up to contains at least 50 times more Fe than As (concentration ratio) and low phosphate concentrations (b1mgL−1), which is a prerequisite for the ability of the sand filter to lower the As concentration in the water to values below50 μgL−1 (Berg et al., 2006).