Assessing the water quality hazard and challenges to achieving the freshwater goal in Sri Lanka.

Nearly 93% of all drinking water supply in Sri Lanka comes from improved sources such as tubewells. Despite this national achievement, deteriorating water quality remains a major challenge to achieving the UN Sustainable Development Goals, particularly SDG 6 ('Clean Water and Sanitation'). In this study, we analyze the state of ambient water quality at the national scale using observational and gridded datasets for both groundwater and surface water quality. We collated single-point, one-off measurements from 1,252 groundwater quality datasets provided by two national agencies in Sri Lanka: the National Water Supply and Drainage Board (NWSDB) and the Water Resources Board (WRB), as no national-scale time-series database on groundwater quality exists. Applying geospatial mapping techniques, we developed a multi-parameter (i.e., chloride, alkalinity, nitrate, nitrite, fluoride, phosphate, total dissolved solids, hardness, iron, and sulphate) groundwater-quality hazard map of Sri Lanka. Our results indicate that 3.6 to 3.8 million people are exposed to poor quality of groundwater that is used primarily for drinking purpose. We also find that surface water quality in some river basins (e.g., Kelani River) is compromised due to contamination from industrial and agricultural activities. We conclude that poor water quality, coupled with a lack of strategic national-scale monitoring system for routine water-quality measurements of both surface water and groundwater, pose a critical barrier to achieving sustainable drinking water supply in Sri Lanka.