Climate resiliency assessment of drinking water technologies in southwest coastal Bangladesh using the 4R framework

Climate change is intensifying hydro-climatic extremes and exacerbating drinking water insecurity in coastal regions. In southwestern coastal Bangladesh, progressive salinisation combined with recurrent disasters threatens safe water access. This study assessed the climate resiliency of six existing drinking water technologies (DWTs), namely community-based rainwater harvesting (CRWH), deep tube wells (DTWs), pond sand filters (PSFs), solar-powered PSFs (SPSFs), desalination plants (DSPs), and ultrafiltration plants (UFPs), in the Bagali Union of Koyra Upazila under Khulna District of Bangladesh. The 4R (robustness, redundancy, resourcefulness, and rapidity) framework was conceptualised through a multicriteria analysis (MCA) to assess the climate resiliency of the DWTs. Data were collected using a mixed-method approach integrating water quality analysis and household surveys with focus group discussions and key informant interviews. Water quality results indicated that DSP delivered the highest quality water, followed by CRWH and UFP, whereas DTW showed excessive salinity (EC = 2601 µS/cm), far beyond the permissible limit. The resiliency ranking differed, where CRWH was the most resilient (0.246), followed by SPSF (0.180), DSP (0.159), PSF (0.149), DTW (0.139), and UFP (0.127). The CRWH benefitted from community participation, active maintenance, and long operational life, whereas DSP and UFP were constrained by energy dependency, high operational cost, and limited local repair capacity. Expanding CRWH within a complementary technology portfolio and strengthening governance mechanisms can significantly increase the climate-resiliency of drinking water supplies in similar hydrogeological and institutional settings across coastal Bangladesh.