The study investigates the human health risks associated with nitrate pollution in the groundwater of the Tehran–Karaj plain, Iran. Using a dataset of over 75 wells sampled annually from 2007 to 2018, the researchers mapped the non-carcinogenic risks of nitrate in the aquifer. The results show that nitrate concentrations varied from 6 to 150 mg/L, significantly exceeding the standard level of 50 mg/L for drinking water. The eastern part of the study region, where children are the most vulnerable age group, experienced higher nitrate levels and non-carcinogenic risks. The number of wells with non-carcinogenic risks increased from 17 in 2007 to 6 in 2018, indicating a potential decline in nitrate levels due to improved sanitation infrastructure. The study highlights the importance of continued efforts to reduce nitrate concentrations below the permissible level to protect the health of the densely populated region.The study investigates the human health risks associated with nitrate pollution in the groundwater of the Tehran–Karaj plain, Iran. Using a dataset of over 75 wells sampled annually from 2007 to 2018, the researchers mapped the non-carcinogenic risks of nitrate in the aquifer. The results show that nitrate concentrations varied from 6 to 150 mg/L, significantly exceeding the standard level of 50 mg/L for drinking water. The eastern part of the study region, where children are the most vulnerable age group, experienced higher nitrate levels and non-carcinogenic risks. The number of wells with non-carcinogenic risks increased from 17 in 2007 to 6 in 2018, indicating a potential decline in nitrate levels due to improved sanitation infrastructure. The study highlights the importance of continued efforts to reduce nitrate concentrations below the permissible level to protect the health of the densely populated region.