Assessment of anthropogenic impacts on the water quality of Mahi River by using water quality index and central pollution control board India framework

Present study aims to assess the water quality of River Mahi in Gujarat, India, a key surface water source. This water body drains into the Arabian Sea along a critical stretch with high anthropogenic pressures. Water samples from three stations, Kadana Dam (S1), Virpur (S2), and Sevalia (S3) were collected monthly throughout the year, 2023. Overall water quality in terms of its physical, chemical and biological characteristic along with its utilization suitablity was evaluated. The physico-chemical parameters like temperature, pH, electrical conductivity (EC), dissolved oxygen (DO), biochemical oxygen demand (BOD), boron (B), calcium (Ca), magnesium (Mg), sodium adsorption ratio (SAR) and biological parameters like total coliform (TC) were analyzed by standard methods. The limits defined by Bureau of Indian Standards (BIS), 2012, Environmental Protection Agency (EPA), 2002 and Central Pollution Control Board (CPCB), India, water quality criteria guidelines, 2019 were used to determine the “designated best use” classification. Using the data obtained from the evaluation of water quality parameters, observed water quality index (WQI) was 31.59 for S1, 30.36 for S2 and 46.63 for S3. In accordance to weighted arithmetic WQI, water quality was classified as “good” at all the three sites. WQI provides general status of water quality which may not be helpful to define water quality in terms of different uses like drinking, irrigation, and industrial etc. Hence, interpretation of WQI along with CPCB designated best use criteria was used to overcome these issues. According to CPCB most water quality parameters were within the permissible limit for drinking water except TC levels, which range from 2 to 49 Most Probable Number (MPN) /100 mL at S1, 39–63 MPN/100 mL at S2, and 39–70 MPN/100 mL at S3. At S1 site water meets CPCB Class A standards for drinking (with disinfection), S2 and S3 falls in Class B/ C category and exhibit elevated coliform levels due to human activities but remain suitable for use after treatment. The calcium (10–48 mg/L), magnesium (14–51 mg/L), boron (0.1–0.5 mg/L) content and SAR level below 26 confirmed that water at all sites was suitable for irrigation. This study demonstrates that combining WQI with CPCB classification offers a robust framework for evaluating water quality for sustainable water resource management and policy development.