Notes

National Water Quality Program
The study estimates that approximately 3.6 to 3.8 million people are exposed to poor groundwater quality, which poses a significant public health risk. Our findings indicate that groundwater quality, particularly in rural areas where it is a major source of drinking water, is often compromised by naturally occurring contaminants and anthropogenic activities. By using a data-driven approach, we created water quality indices (WQI) and groundwater-quality hazard maps, revealing significant spatial variability in water quality across the country, with millions of people exposed to substandard groundwater. This study provides the first comprehensive national-scale assessment of water quality in Sri Lanka, focusing on both surface water and groundwater. We find that groundwater quality is comparable between the two national agencies.
Water-quality hotspots focused on five major parameters that were tracked by the Sustainable Development Goal (SDG) Indicator 6.3.2 (Proportion of bodies of water with good ambient water quality) and considered the most critical for surface water quality. Surface water-quality parameters (e.g., nutrients) were also found to be above the permissible limits recommended by the World Health Organization (WHO), the US Environmental Protection Agency (EPA), and Sri Lanka’s standards for drinking water. It should be noted that tap water through piped network can originate from both groundwater and surface water sources, following treatment. According to Sri Lanka’s 2012 Census of Population and Housing, the coverage of household drinking water sources is 46% (total of 5.2 million households) by protected dug wells (i.e., groundwater), 30% by tap waters and 5% by surface water sources (Fig. 1b). In Sri Lanka, both surface water and groundwater resources are widely used for domestic, commercial, and industrial purposes, and small-scale irrigation.
Point source pollution originates from a specific, identifiable source, such as a factory discharging waste directly into a river. From agricultural runoff laden with fertilizers to industrial discharge containing toxic chemicals, the sources of water contamination are diverse and widespread. Agriculture is a major contributor to water pollution through fertilizer and pesticide runoff, soil erosion, and animal waste. Industries can reduce their footprint by implementing cleaner production technologies, investing in advanced wastewater treatment systems, reusing and recycling water, and adopting closed-loop systems. It can be prevented by reducing nutrient runoff from agricultural and urban areas, improving wastewater treatment, and restoring riparian buffers.
The harmful cyanobacterial blooms found in 17 freshwater reservoirs in Sri Lanka46. Long-term (2003–2016) changes in Chemical Oxygen Demand (COD) in 12 monitoring sites along Kelani River in Sri Lanka. The entire Kelani River Basin was found to be contaminated with total coliform bacteria and Escherichia coli(E. coli) bacteria that best indicate fecal pollution and the possible presence of pathogens44. Figure 4 shows temporal changes in monthly Chemical Oxygen Demand (COD) measurements in Kelan River at 12 locations along the river.
Liyanage and Manage53 reported that surface and groundwater in the Kelani River catchment are a possible reservoir of two antibiotics, namely, penicillin and tetracycline and their resistance genes. Groundwater multi-parameter hazard index and population exposure maps of Sri Lanka. Groundwater multi-parameter hazard index map (Fig. 8a) is created using the sum of all hazard index scores at all gird points within each district.
A District-wise WQI scores and classification of groundwater based on the Sri Lanka drinking water standards. Results show that only a few districts in Sri Lanka present very good to good quality groundwater sources. We also calculate summary statistics of each groundwater-quality parameter within the aquifer units, climate zones and districts (see supplementary Tables S6-8). For mapping, we interpolate groundwater parameters at the national scale using geostatistical interpolation algorithms in ArcGIS Desktop software (v.10.8). Groundwater quality in Sri Lanka is highly variable (Fig. 5) within the country but appears to be controlled by climate and geology and the distribution of aquifer systems (see aquifers in Sri Lanka in Fig. 5k and supplementary Fis. S18). Geostatistically interpolated maps of mean annual rainfall and mean (1992–2010) surface water-quality parameters across Sri Lanka.
Associations between geology, aquifer types, and groundwater quality need to be studied in detailed to characterize the origin and evolution of water quality in Sri Lanka. Several adverse health outcomes are reported to be linked to drinking water intake that comes from poor-quality groundwater. Shallow sandy and alluvial aquifers, and fractured Regolith aquifer (see Fig. S18) in the north are particularly low in ambient groundwater quality in Sri Lanka. We have not produced a groundwater quality risk map in this study due to the lack of information on actual groundwater users (exposure) and vulnerability (e.g., access to wells).
The denotation simply points to the process of making water better, but the substance of this improvement is profound, touching every facet of our existence. The import of this endeavor is therefore immense, impacting everything from public health to economic sustainability. Its sense lies in the interconnectedness of water with all aspects of life. The elucidation process involves detailing these standards and the steps needed to achieve them.
Technological advancements play a crucial role in improving water quality. Achieving better water quality requires a combination of preventative measures and remedial actions. Accurate data allows us to pinpoint pollution sources, assess the effectiveness of interventions, and adapt our strategies as needed. This involves setting thresholds for various pollutants, considering ecological health, and guaranteeing safe drinking water for all populations.
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Sharing knowledge, technology, and financial resources can also support developing countries in improving their water quality. The interpretation of water quality data expands to include ecological indicators, biodiversity metrics, and resilience assessments. The interpretation of data from water quality monitoring becomes central to guiding interventions. To offer clarification, consider the difference between drinking water standards and recreational water quality. The open access data on surface water quality of the Kelani River by the Central Environmental Authority (CEA) is duly acknowledged. Monitoring systems should include a focus on key contaminants like fluoride, nitrate, and iron, and consider the potential exacerbation of water quality issues due to climate change and increased industrial activities.
The import of overcoming these challenges is substantial for ensuring long-term water security and environmental health. The sense of urgency is growing with increasing water scarcity and pollution. Clarification is needed on the different types of water treatment technologies and their appropriate applications.
In this study, a simple method is developed (see Eq. 1) to create a geospatial groundwater-quality hazard map using the NWSDB groundwater quality dataset that has 688 data points. To address this limitation, we developed a groundwater-quality hazard index based on chemical parameters that do not meet drinking water standards. Multi-parameter groundwater-quality hazard index in created using available datasets and population exposure to poor groundwater quality is estimated at the district level.
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