The Groundwater in 13 districts of Bihar has been reported to be contaminated by excessive quantity of Arsenic. All these districts are located on the banks of various rivers and comprise of Patna, Bhagalpur, Buxar, Vaishali,Begusarai, LAkhisarai, Munger, Katihar,Bhojpur, Khagaria, Saran, Darbhanga and Samastipur.
Groundwater through Tubewell is one of major source of Drinking Water in Bihar.
A Survey conducted by Public Health Engineering Department has established this fact. The Survey was undertaken in districts where the percentage of  Surface Water bodies contaminated with Arsenic exceeded 15%.
The acceptable level as defined by WHO for maximum concentrations of arsenic in safe drinking water is 0.01 mg/L  however Arsenic concentrations of more than  0.05 mg/L has been reported in these areas.
The Government is undertaking a series of steps to afford Pure and Hygienic drinking water to the residents in these districts. These include Water Supply from Rivers in Urban Areas apart from Handpumps and Treatment units in both rural and urban areas. It has also launched multi-village scheme to provide arsenic-free water to the people. Under the scheme, underground water would be purified and supplied to the villagers, he said.
Arsenic contamination of groundwater is often due to naturally occurring high concentrations of arsenic in deeper levels of groundwater. It is a high-profile problem due to the use of deep tubewells for water supply causing serious arsenic poisoning to large numbers of people.
In an independent Study conducted by researchers of Harvard University in 2012, the presence of arsenical skin lesions, consistent peripheral  motor and sensory neuropathy as well other neurological abnormalities have been reported in the arsenicosis patients of Bihar. They had also observed an apparent increase in fetal loss and  premature delivery in the women with the elevated level of arsenic in their drinking  water.
The Researchers also warned that  many villagers might be sub-clinically affected and they are continuing drinking the contaminated water since they are mostly unaware of the problem.