Fluoride
Long use stains and pits teeth (dental fluorosis) and can stiffen bones and joints (skeletal fluorosis).
Fluoride affected districts in Tamil Nadu
21 districts of Tamil Nadu had at least one groundwater sample with fluoride above the BIS drinking water limit (over 1.5 mg/l) in CGWB's pre-monsoon 2023 tests. Across the state, 9.72% of 916 samples were over 1.5 mg/l.
Districts affected
| District | Samples over the limit | Also found |
|---|---|---|
| Ariyalur | At least one | – |
| Chennai | At least one | Salinity (high TDS) |
| Coimbatore | At least one | Salinity (high TDS) |
| Cuddalore | At least one | – |
| Dharmapuri | At least one | Salinity (high TDS) |
| Dindigul | At least one | Salinity (high TDS) |
| Erode | At least one | Salinity (high TDS) |
| Karur | At least one | – |
| Krishnagiri | At least one | Salinity (high TDS) |
| Madurai | At least one | – |
| Namakkal | At least one | Salinity (high TDS) |
| Perambalur | At least one | Salinity (high TDS) |
| Pudukkottai | At least one | Salinity (high TDS) |
| Salem | At least one | Salinity (high TDS) |
| Theni | At least one | Salinity (high TDS) |
| Thoothukudi | At least one | Salinity (high TDS) |
| Tirunelveli | At least one | Salinity (high TDS) |
| Vellore | At least one | Salinity (high TDS) |
| Villupuram | At least one | Salinity (high TDS) |
| Virudhunagar | At least one | Salinity (high TDS) |
| The Nilgiris | At least one | Salinity (high TDS) |
Making the water safe
RO or activated alumina filters remove fluoride; rainwater, which has almost none, is a safe drinking source when stored clean.
Cleaner water from the rain
Rainwater has almost no dissolved salts or fluoride. Stored clean it is safe drinking water, and recharged it slowly freshens the aquifer.
Frequently asked questions
Which districts of Tamil Nadu have fluoride groundwater?
CGWB's 2024 report found fluoride above the limit in groundwater samples from 21 districts of Tamil Nadu: Ariyalur, Chennai, Coimbatore, Cuddalore, Dharmapuri, Dindigul, Erode, Karur, Krishnagiri, Madurai, Namakkal, Perambalur, Pudukkottai, Salem, Theni, Thoothukudi, Tirunelveli, Vellore, Villupuram, Virudhunagar, The Nilgiris.
Is it safe to drink borewell water in these districts?
Not without testing. Water from one borewell can be fine while the next is not. Test at a NABL-accredited lab or the Public Health Engineering department, and treat it if it fails. RO or activated alumina filters remove fluoride; rainwater, which has almost none, is a safe drinking source when stored clean.
Source: Annual Ground Water Quality Report 2024 (Report on Groundwater Quality of Shallow Aquifers in India 2024), Central Ground Water Board. Sample counts are given only for the districts CGWB lists among the worst affected.