New Delhi: Over 20% of groundwater samples collected in Delhi in 2023 had nitrate levels exceeding the permissible limit of 45 mg/l, according to a submission by Central Groundwater Board (CGWB) before the National Green Tribunal (NGT). In some locations, nitrate levels peaked at 994 mg/l, more than 22 times the safe limit.
In Delhi, high levels were detected in seven of the 11 districts — New Delhi, North, Northwest, South, Southeast, Southwest, and West Delhi. Nitrate contamination is a significant environmental and public health concern, especially in agricultural regions where nitrogen-based fertilisers and animal waste are commonly used. Elevated nitrate levels in groundwater can cause methemoglobinemia, or blue baby syndrome in infants. Although adults can tolerate slightly higher concentrations, the specified limits must not be exceeded. “If the limit is exceeded, water is considered unfit for human consumption,” it said. Studies have also shown that high nitrate levels pose risks such as cancer, thyroid disorders and acute oxygen deficiency. Delhi was the fifth worst affected among states or Union territories in peak nitrate concentration. Andhra Pradesh has recorded the highest level in the country. Nitrate concentrations there have reached 2,296.36 mg/l. Delhi is ranked eighth overall in terms of the percentage of samples exceeding the safe limit. About 20.39% — or one in every five groundwater samples collected in the capital — contained nitrate levels above the permissible limit. Rajasthan is the worst on the scale of pervasiveness, with 49.52% of its 630 samples exceeding safe limits. This submission was made in an ongoing case after NGT in Jan took suo motu cognisance of a news report highlighting high nitrate levels in groundwater across several districts in the country. The report, citing CGWB data, said excessive nitrate levels were found in groundwater in 440 districts, up from 359 districts in 2017. In an affidavit dated Dec 22, CGWB referred submitted its annual groundwater quality report for 2024, which were based on samples collected in 2023. It said that a detailed national groundwater quality assessment would be released in Sept 2026. CGWB pointed out that while the monsoon rains usually improve groundwater quality, they can worsen nitrate contamination due to agricultural runoff. “Following the monsoon season, nitrate concentrations often increase due to surface runoff from agricultural fields. During heavy rainfall, fertilisers and other contaminants can wash into aquifers, elevating nitrate levels,” the report said. Data showed that 30.77% of samples exceeded permissible nitrate limits in the pre-monsoon period, rising slightly to 32.66% post-monsoon.
