The important toxic elements like fluoride and arsenic are creating more hazardous in many parts of the country. Fluoride is a major, naturally occurring contaminant in drinking water in many regions. At low levels, say 1 mg/l, it is found to be beneficial and high levels can cause structural tooth damage and at a high enough level can cause skeletal damage. The arsenic contamination invariably arises from natural geological and environmental conditions. Arsenic arises in many ores and minerals and is frequently present in combination with iron and manganese oxides; under various natural conditions it can be rendered soluble and released into the groundwater. The problem is especially acute in the Ganges delta region, where the arsenic is believed to be associated with the iron and manganese oxides in the alluvial sediments.