Integrated catchment and treatment strategies for safeguarding drinking water quality: an adaptive decision-making tool

Ensuring the safety and sustainability of drinking water sources is a critical component of modern water resource management. The recast Drinking Water Directive (EU 2020/2184) emphasizes the delivery of safe drinking water by strengthening protections along the entire supply chain, from source to tap, and adopting a risk-based approach to water safety as recommended by the World Health Organisation. Assessments of water treatment costs tend to focus on the current level of treatment, and not the potential additional costs associated with treatment of new emerging contaminants, many of which are of low molecular weight requiring specialist treatment technologies with expensive CAPEX and OPEX costs. The impacts of climate change on the raw water quality source water abstractions are also likely to result in increasing costs of water treatment systems. In Ireland, the inclusion of emerging substances on the 2023 Drinking Water Regulations and on the first European Commission’s Watch List reflects the evolving nature of water safety management in response to pollutants of emerging concern and environmental pressures. This study presents a robust methodology with a view to inform future funding and targeting of water quality measures and source protection work. Applied across six case studies, the four-stage process (pre-screening, coarse screening, fine screening, and final comparative analysis) guides decision-making. The framework incorporates open-source data from the Environmental Protection Agency (EPA) of Ireland, including land-use maps, Water Framework Directive (WFD) waterbody status and significant pressures such as agriculture, forestry, industry, and hydro-morphology, alongside local pressures on water sources. Source protection measures and treatment technologies were derived from extensive literature review of national and international projects and were tailored to specific goals for each case study, with independent evaluations for both strategies. The process concludes with a comparative analysis to identify optimal solutions for each scenario. The study provides recommendations, based on economic assessments and the evaluation of environmental and technological gaps to support the stakeholders in decision making and policy development. The selected strategy for each case is dependent on a suite of site-specific features, including the raw water source type, the catchment size, the mapped WFD pressures exerted into the water source and the latest WFD status and the Water Treatment Plant capacity. The findings highlight the importance of adopting integrated approaches to ensure the resilience of drinking water systems in the face of future uncertainties.