CHENNAI: 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 Prabu Babu and Saurabh Chandra Maury of the Vellore Institute of Technology (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).
Electrical conductivity across the city showed extreme variance, peaking at an alarming 13,088 microsiemens per centimetre. Researchers noted that such high values point directly to severe seawater intrusion along coastal stretches, exacerbated by heavy extraction and sewage ingress.
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.
To ensure higher precision, the VIT team paired conventional index methods with an advanced statistical model (TRFN AHP) designed to account for field uncertainties and subjective expert judgment. Combined with Geographic Information System (GIS) mapping, the approach achieved over 86% predictive accuracy in plotting spatial contamination patterns across Chennai.
Warning that single-year sample data from 2022 cannot capture long-term seasonal shifts, the researchers called for multi-year monitoring. They recommended immediate state action to protect natural recharge zones, strictly regulate chemical fertilisers, and upgrade municipal wastewater treatment infrastructure.