Potential source water protection measures to mitigate against organic matter based on its pathway and process of contamination using Ireland as a case study.

Dissolved organic matter (DOM) is found across all freshwater systems and originates from soils, leaf litter and leachate from plant material and the decomposition processes. However, as a consequence of a combination of changes in both land use practices and climate change there has been a recorded increase in DOM export in freshwater systems over the last number of years. High concentrations of Dissolved Organic Matter (DOM) in water react with chlorine during treatment, forming harmful disinfection by-products (DBPs) such as trihalomethanes (THMs) and chloroform. There are numerous options available to mitigate and treat DBPs as part of the water treatment process, including a range of technologies and management procedures which aim to reduce contact between DOM precursors and disinfectants. Nevertheless, protection of the water at source represents an alternative and likely additional activity which could act to reduce DBP formation in drinking water in a more cost effective and efficient way.

Source Water Protection (SWP) through the use of Nature Based Solutions and other methodologies has been widely implemented in many regions of the world to improve raw water quality. However, compared with other potential contaminants such as microbial pathogens, very little work has specifically focused on the reduction of DOM input to water treatment plants. This study examines the potential effectiveness of SWP measures at reducing organic matter with the aim of minimising human exposure to DBPs in drinking water. A review was undertaken to identify SWP measures considered most likely to mitigate against DOM, pinpointing five key land use categories linked to DOM loading: forestry, peatland, agriculture, lakes/reservoirs, and wastewater treatment. Measures were assessed based on their proven effectiveness at reducing DOM or other relevant pollutants. Input was gathered from the Irish water sector via a focus group and survey to evaluate the feasibility of implementing these measures at catchment scale. The findings suggest there is a potential role for SWP for the mitigation of DOM in source water leading to improved DBP management in conjunction with treatment plant improvements and upgrades. However, there is currently a lack of evidence-based research demonstrating the effectiveness of SWP measures in mitigating against DOM and DBP formation which is a significant barrier to the uptake and implementation of such measures. In addition, active and participatory approaches to education and support in this area will encourage stakeholders to shift their perception from an end of pipe only solution to a multi-barrier approach to reduce the overall risk of DBP contamination of drinking water.