The Nakuru government has given borehole owners 14 days to get clearance certificates from the public health department before selling water.
Public health chief officer Samuel King’ori said underground water contains fluoride levels higher than the 1.5mg per litre recommended by the World Health Organization.
“The fluoride destroys parts of the body, especially the skeleton and teeth,” he said in his office on Friday.
The most affected areas are Gilgil, Elementaita, Naivasha, Nakuru and Rongai, with some places having 30mg of fluoride.
“The borehole owners should give us a borehole operator medical certificate and water analysis certificate from a recognised institution,” King’ori said.
He said infants are most affected by fluoride.
“Depending on the quantity of the fluoride, the effects may begin to show two years after one starts consuming the water,” King’ori said.
He said the effects of fluoride are only preventable and cannot be reversed.
“Skeletal fluorosis develops slowly and can cause deformation,” King’ori said.