Fluoride is often called a two-edge sword – in small dosages, it has remarkable influence on the dental system by inhibiting dental carries, while in higher dosages causes dental and skeletal fluorosis. When present in concentration of 0.8-1.0 mg/L, fluoride is beneficial for calcification of dental enamel especially for the children below 8 years of age. At higher concentrations (1.5-2.0 mg F/L), fluoride effects adversely and leads to dental fluorosis. At still higher concentration, (3-6 mg F/L) skeletal fluorosis occurs. The disease affects the bone and ligaments.  Intakes of 20-40 mg F/day over long period have resulted in crippling skeletal fluorosis.

High concentrations of fluoride in ground water are common in some of the semi-arid areas of Rajasthan, southern Punjab, Gujarat, Karnataka, Tamil Nadu, Madhya Pradesh, and southern Haryana. Several areas of Andhra Pradesh have high concentrations of fluoride in ground water (exceeding 5 mg/l). There are a number of cases of dental and skeletal fluorosis in these areas. In several parts of Karnataka, Tamil Nadu, U.P., and other areas, fluoride concentrations of groundwater are more than the permissible level of 1.5 mg/l. An extensive survey of the community water supplies has shown that around 25 million people in rural areas consume water with fluoride content more than this limit. Various authorities have given permissible limits for fluoride content in drinking water. Concentrations of fluoride in drinking water in different parts of the country varies from 0.5 to 50 mg/L.

 Permissible limit of fluoride in drinking water prescribed by various organizations

Fluoride contaminated ground water is creating health problems in India. Nearly 90 million people including 6 million children in the country in 200 districts in 15 states are affected with dental, skeletal and/or non-skeletal fluorosis. The extent of fluoride contamination in ground water varies from 1.0 to 48 mg/l. The fluoride affected states are: Andhra Pradesh, Bihar, Delhi, Gujarat, Haryana, Jammu and Kashmir, Karnataka, Kerala, Madhya Pradesh, Maharashtra, Orissa, Punjab, Rajasthan, Tamil Nadu, and Uttar Pradesh,

In Rajasthan, in the absence of perennial rivers, surface and canal systems, ground water remains the main source of drinking water for about 95% population. Ground water of 18 districts contains high fluoride (2 to 20 mg/l) affecting approx. 3 million people. Studies have revealed that three million people in the state are consuming water with excess fluoride. Rajasthan has to depend on ground water resources to a greater extent and in arid in semi-arid areas, the ground water is the only water resource for drinking as well as agricultural purposes. According to the survey of states for drinking water supply in rural habitation conducted by the Rajiv Gandhi Drinking Water Mission, 9,741 villages and 6,819 habitations have fluoride content more than 1.5 mg/l in ground water.

In Tamil Nadu, fluoride monitoring is carried out at 1286 observation wells by TWAD Board throughout the State twice in a year – during pre-monsoon and post monsoon periods. About 121 blocks in 19 districts are found to have high fluoride concentration in ground water.