New Delhi, Dec. 27 -- More than 20% of groundwater samples tested in Delhi contained nitrate levels above the permissible limit of 45 mg/l, with some samples reaching up to 994 mg/l - over 22 times the safe standard - according to data submitted by the Central Groundwater Board (CGWB) to the National Green Tribunal (NGT). With a peak reading of 994 milligrams of nitrates per litre of drinking water, Delhi fared as the fifth worst-affected state or Union territory for high nitrate contamination, read the report. Andhra Pradesh fared the worst with nitrate levels touching a peak of 2,296 mg/l, it showed. While 20.39% of Delhi's samples exceeded safe limits (eighth-worst among states and UTs), Rajasthan recorded the highest proportion of contaminated samples at 49.52%. In total, high nitrate levels were found in seven out of Delhi's 11 districts, including New Delhi, north, northwest, south, southeast, southwest and west Delhi, it said. Nationally, the number of districts with excessive nitrate levels rose from 359 in 2017 to 440 in 2023. "The consolidated national groundwater quality assessment report will be published in September 2026.," it stated. The findings are part of CGWB's 2024 annual groundwater report, based on samples collected in 2023. The submission was made as part of an ongoing case, after NGT took suo motu cognisance of a news article in January 2025. The report added nitrate contamination in groundwater remains a significant environmental and public health concern, particularly in agricultural regions where use of nitrogen-based fertilizers and animal waste is prevalent. "Elevated nitrate levels can lead to methemoglobinemia (blue baby syndrome) in infants. If the limit is exceeded, water is considered to be unfit for human consumption," it said. Nitrate pollution, often linked to agricultural runoff from nitrogen-based fertilizers and animal waste, poses serious public health risks. Studies have shown that exposure to high levels of nitrates are associated with long-term risks such as cancer, thyroid disorders, and oxygen deficiency. CGWB said while monsoon rains typically improve water quality, it can have the opposite effect for nitrate levels - which can shoot up due to agricultural run-off. Priti Mahesh, an environment and public health researcher said leaching from poorly managed septic tanks and sewage systems was another way of contamination....