<prompt> In drinking water, recommended fluoride level is___ ppm0.50.5-0.81.51.1  <response>: Ans. b 0.5-0.8 ppm Ref. Parks textbook of PSM - 22nd511, 582 The permissible concentration of fluorides in drinking water is0.5 to 0.8 mgL Drinking water is known to protect gainst dental caries with Fluoride content at about1 mglitre Mottling of dental enamel reported at levels above1.5 mgL intake. Endemic fluorosis has been observed when the drinking water contain excess fluorine i.e.3-5 mgL Skeletal FluorosisGenu valgum is observed when the lifetime daily intake of fluorine is of3.0-6.0 mgL.ENDEMIC FLUOROSIS Certain parts e.g., Andhra Pradesh, Punjab, Haryana, Karnataka, Kerala, and TN are known for endemic flurosis. Dental Fluorosis: Ingested during the years of tooth calcification essentially during the first 7 years of life. Mottling is best seen on the incisors of the upper jaw. Prevention: Changing the water source. Nalgonda technique for defluoridation of water.The presence of following chemicals in excess of prescribed limits may constitute ground for rejection of the water as a source of public water supply:A. Inorganic constituents: Arsenic: recommended maximum limit of concentration is 0.01 mgL. Cadmium 0.003 mgL maximum limit. Chromium Cyanide: maximum limit 0.07 mgL. Fluoride Should not be more than 1.5 mgL Lead Mercury: 0.001 mgL minimum upper limit. Bacterial plate count on yeast extract agar after incubation at 22degC for 7 days might serve as the best general-purpose indicator of microbiological quality. Selenium Nitrite and Nitrate: When nitrate level in drinking water exceeds 50 mgL, methemoglobinemia may occur; most susceptible are bottle-fed infants of less than 3 months. Nitrate is good indicator for past contamination.B. Organic constituents Polynuclear aromatic hydrocarbons and Pesticides 