Water scarcity in the hill tract districts of Bangladesh becomes acute in the dry season as most of the streams, the primary source of water, dry up. However, groundwater, where available, can supply water throughout the year. In this study, a total of 37 water samples were collected and analyzed from shallow (34) and deep (3) wells in Khagrachhari Sadar to assess their geochemical type and suitability for drinking using a multiparameter groundwater quality index (GWQI), as well as their suitability for irrigation uses using the sodium adsorption ratio (SAR), residual sodium carbonate (RSC), sodium percentage (SP), and the Riverside and Wilcox classifications. The physicochemical parameters of the groundwater were characterized by relatively low EC, low pH, positive redox potentials (Eh) in millivolts, and mostly soft water. Shallow wells were dominated by Ca–HCO₃- and Ca–Na–HCO₃-type water, and deep wells by Na–HCO₃-type water. Among major and trace ions, there were higher concentrations, exceeding safe water standards, of HCO₃⁻ in deep wells and NO₃⁻, Fe²⁺, and Mn²⁺ in shallow wells. Irrigation water quality assessments and GWQI results reveal that most shallow wells can be considered good and safe options for both drinking and irrigation, while groundwater from deep wells requires additional caution prior to use for agricultural purposes.

The acute scarcity of safe water exists in disaster-prone coastal Bangladesh due to the occurrences of brackish or saline and arsenic contaminated groundwater, the salinization of freshwater ponds by inundation during storm surges, and brackish water aquaculture. Millions of people living there mainly depend on pond water and rainwater harvesting system and face severe difficulties to collect freshwater, particularly during the dry season. Therefore, various community water supply technologies, e.g., RO, SIDKO, RPWS, SkyHydrants etc. have been established to meet their daily needs, though the majority of these technologies fall short of the value of time and effort of water collection and sometimes fail to supply water of desired quality. Managed Aquifer Recharge (MAR) technique, also a community water supply system, was designed to provide safe water by creating underground storage of freshwater where ambient groundwater salinity is reduced by infiltrating rooftop or pond water through wells. Understanding the need to sort out the best water supply option, a comparative study has been conducted between MAR and other water supply technologies, and among all of them the MAR has been demonstrated as a low cost, reliable, sustainable, and durable option for providing safe drinking water to the community round the year. The Dhaka University Journal of Earth and Environmental Sciences, Centennial Special Volume June 2022: 157-166