1 in 3 groundwater samples in Chennai unsafe to drink: Study

Nearly one-third of groundwater sampled across Chennai is poor, very poor, or completely unsuitable for drinking, finds a new assessment that highlights the vulnerability of the city’s groundwater resources to contamination and inadequate water management.
The study, conducted by VIT, Chennai — and published in the journal Applied Water Science on September 6, 2026 — evaluated groundwater samples from 39 wells using 12 critical quality parameters, including total dissolved solids, nitrates, calcium, sulphate, fluoride, and electrical conductivity. The samples were collected between January and December 2022, and obtained from the State Ground and Surface Water Resources Data Centre.
Among the 39 sampled areas, Taramani emerged as the most severely degraded location, registering a Water Quality Index (WQI) score of nearly 700 — more than double the maximum permissible safety threshold of 300 for drinking water.
The findings reveal that under advanced predictive modelling, barely 7.1% of tested samples qualified as excellent. Around 62.8% were rated good, while 25.9% were deemed poor, 0.7% very poor, and nearly 3.5% unsafe for human consumption. (Under the standard-weight WQI, the same was 7.9% excellent, 65.8% good, 21.7% poor, 1.9% very poor and 2.6% unsafe).
The deteriorating quality stems from a combination of adverse hydrogeological conditions and aggressive human activity. Natural recharge is restricted by shallow aquifers, clay layers, and limited rock fractures. At the same time, unchecked groundwater extraction, untreated sewage, leaking septic tanks, open drains, and unregulated fertiliser use accelerate the accumulation of contaminants.