Ground water contamination has become very important issue of concern these days. People of Bihar mostly use ground water sources for household and agricultural needs. In Mohuddinagar block people are dependent on agriculture for their livelihoods and groundwater was the major source. An inclusive assessment of ground water resources was done in the study area from 12 station points in the month of November,2021. The study was done to understand hydrogeochemical facies of groundwater along with the suitability of groundwater in household and for agricultural needs. The physio chemical parameters of water including EC (Electrical conductivity), TDS (Total dissolved solids), pH, major cations and and anions was investigated. The outcomes were compared with the Bureau of Indian Standards-2012. Among heavy metals Arsenic and Iron were tested in water samples and the map showing the distribution of these heavy metals was created. The analysis of samples was done based upon APHA standard methods. Piper trilinear diagram and Chadha’s plot represented different hydrogeochemical facies of the groundwater. The SAR, Na% and RSC values were calculated to assess its suitability for agricultural purposes. Most of the statistical operations were done using MS-EXCEL software. Except few all the major ions were found to be present within the prescribed limits of Bureau of Indian Standards-2012. As and Fe concentration at some sampling locations was found to be beyond the permissible limits. In the study area Mg²⁺ - Ca²⁺ − HCO₃^- and Mg²⁺ -HCO₃^—Cl^- were dominant hydro chemical facies. For agriculture purpose 50% of the water samples had high salinity and it needs to be managed before use in irrigation, it is represented by US salinity diagram. Wilcox plot represented the relation between Na% and EC and it was concluded that groundwater of study area falls under following categories:

• Excellent to good
• Good to permissible quality and so it can be used for irrigation purposes.