Arsenic contamination of groundwater is widespread and there are a number of regions where arsenic contamination of drinking-water is significant. Thousands of people have already been identified to be affected by arsenic poisoning, in addition to the millions potentially under threat from drinking contaminated water. Provision of arsenic free water is urgently needed for immediate protection of health and well being of the people living in arsenic affected areas. In most situations, substitution of tube well water by an alternative safe and reliable source of water supply is not an easy task. The symptoms and signs caused by long-term elevated exposure to inorganic arsenic differ between individuals, population groups and geographical areas. Thus, there is no universal definition of the disease caused by arsenic. This complicates the assessment of the burden on health of arsenic. Microorganisms such as Thiobacillus ferrooxidans, Lepto spirillum ferrooxdans and fungi like Scopulariopsis previcaulus, Penicillum sp., Gliocladium roseum, and yeast Candida humicola have been shown to oxidize As (III) to less toxic form As (V).