Assessing Groundwater Quality in Prayagraj City: Spatial Patterns of pH, Hardness, TDS and Major Ions

Abstract

Tube wells supply about 77% of Prayagraj’s piped water, so the chemical quality of its groundwater bears directly on public health and on the condition of its water infrastructure. This study examines ten parameters (temperature, pH, total hardness, turbidity, dissolved oxygen, total dissolved solids (TDS), calcium, magnesium, chloride and bicarbonate) at 16 sites in Prayagraj city and compares them with the Indian drinking-water standard IS 10500:2012 and WHO guidance. pH (7.2–7.8) and chloride (49–94 mg/L) met the standards at every site. Hardness (198–329 mg/L), TDS (341–811 mg/L), calcium, magnesium and alkalinity exceeded the acceptable limits at most sites, but none exceeded a permissible limit. Turbidity (0.9–7.1 NTU) was the only parameter above a permissible limit, at six sites, and every site exceeded the acceptable limit for at least five of the seven parameters assessed. A weighted-arithmetic water quality index ranged from 20.7 to 103.3, placing one site in the excellent and two in the unfit class, with turbidity supplying about three-quarters of the index value on average. Civil Lines had the highest TDS and magnesium and the lowest dissolved oxygen, whereas Allenganj had the lowest TDS but the second-highest turbidity, so no part of the city is uniformly better. TDS was significantly correlated only with magnesium (r = 0.56, p = 0.024). The results indicate a water resource that is usable under BIS provisions yet falls short of acceptable limits almost everywhere, and they point to turbidity control, selective treatment, wider parameter coverage and repeated, georeferenced monitoring as priorities.