Salinity (high TDS)
Water tastes salty or brackish, scales pipes and geysers, and is unfit to drink untreated.
Saline groundwater (high TDS) districts in Tamil Nadu
23 districts of Tamil Nadu had at least one groundwater sample with salinity (high TDS) above the BIS drinking water limit (EC over 3,000 µS/cm, roughly TDS over 1,900 mg/l) in CGWB's pre-monsoon 2023 tests.
Districts affected
| District | Samples over the limit | Also found |
|---|---|---|
| Chennai | At least one | Fluoride |
| Coimbatore | At least one | Fluoride |
| Dharmapuri | At least one | Fluoride |
| Dindigul | At least one | Fluoride |
| Erode | At least one | Fluoride |
| Kancheepuram | At least one | – |
| Krishnagiri | At least one | Fluoride |
| Nagapattinam | At least one | – |
| Namakkal | At least one | Fluoride |
| Perambalur | At least one | Fluoride |
| Pudukkottai | At least one | Fluoride |
| Ramanathapuram | At least one | – |
| Salem | At least one | Fluoride |
| Theni | At least one | Fluoride |
| Thoothukudi | At least one | Fluoride |
| Tiruchirappalli | At least one | – |
| Tirunelveli | At least one | Fluoride |
| Tiruvallur | At least one | – |
| Thiruvarur | At least one | – |
| Vellore | At least one | Fluoride |
| Villupuram | 8 of 48 | Fluoride |
| Virudhunagar | At least one | Fluoride |
| The Nilgiris | At least one | Fluoride |
Making the water safe
Reverse osmosis (RO) removes dissolved salts; recharging fresh rainwater dilutes salinity in the aquifer over time.
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 saline (high TDS) groundwater?
CGWB's 2024 report found salinity (high TDS) above the limit in groundwater samples from 23 districts of Tamil Nadu: Chennai, Coimbatore, Dharmapuri, Dindigul, Erode, Kancheepuram, Krishnagiri, Nagapattinam, Namakkal, Perambalur, Pudukkottai, Ramanathapuram, Salem, Theni, Thoothukudi, Tiruchirappalli, Tirunelveli, Tiruvallur, Thiruvarur, 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. Reverse osmosis (RO) removes dissolved salts; recharging fresh rainwater dilutes salinity in the aquifer over time.
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.