Drinking water quality surveillance in Bhutan: trend and compliance (2017-2024).

Clean and safe drinking water is essential for public health. Despite substantial infrastructure investments, ensuring water safety remains a challenge in Bhutan. The objective of the study is to provide a nationwide assessment of drinking water quality from 2017 to 2024, covering 20 dzongkhags samples from 31 urban (n = 20,982) and 242 rural (n = 14,361) surveillance sites. Data were retrieved from the Water Quality Monitoring Information System and analyzed for compliance with Bhutan Drinking Water Quality Standards and WHO guidelines. Only 52.8% of urban samples met the microbial standard (0 CFU/100 mL), with the Eastern region showing the lowest compliance. Residual chlorine compliance was critically low (11.9%), indicating inadequate disinfection. While turbidity met Bhutan's standard (95.2%), only 67.3% complied with WHO's health-based guideline (1 NTU). Other parameters, such as pH and conductivity, showed high compliance (>96%). Rural systems, largely untreated, showed better microbial compliance (70.1%), though methodological differences limit direct comparison. Health risk classification showed seasonal deterioration in safety, particularly during the monsoon in urban and rural areas. The study recommends shifting to risk-based water safety management, including upgrading treatment capacity, standardizing testing methodology, and implementing and auditing water safety plans to meet Bhutan's Five-Year Plan targets and Sustainable Development Goal 6.