Source Risk Assessment and Management

The revised Drinking Water Directive (DWD) (2020/2184) was transposed into national law in March 2023 with the European Union (Drinking Water) Regulations 2023 (S.I. No. 99 of 2023) (DWR). Under the DWR there is a requirement for a comprehensive risk assessment and risk management approach that encompasses all steps in water supply from catchment to consumer, with the inclusion of the requirement for catchment or raw water monitoring. 

In 2024 the Department of Housing, Local Government and Heritage published a guidance document which provides a framework for a national approach to Drinking Water Source Protection. This framework builds on the practices already in place and allocates responsibility for the various actions to the relevant stakeholders. The guidance was developed to support the implementation of the DWR and is complementary to the overall Water Framework Directive implementation process.

Uisce Éireann (UÉ) is identified as the responsible body for undertaking the risk assessment and coordinating risk management for drinking water catchments associated with public water supplies. The risk assessment and risk management of all drinking water sources must be completed by July 2027 for the first time and every six years thereafter. 

Drinking Water Safety Plan 

UÉ has adopted the Drinking Water Safety Plan (DWSP) approach which is in line with the DWR and Drinking Water Source Protection Guidelines. This approach was first developed by the World Health Organisation (WHO) in 2004 and the guidelines were updated 2023. The approach seeks to protect human health by identifying, assessing and managing risks to water quality and quantity; taking a holistic approach from source (catchment) to tap (consumer). 

UÉ commenced the development of a new evidence-based approach to DWSPs for all water supply zones in 2018 and this work is still ongoing. It is a multi-barrier approach to managing risk to drinking water, takes a source to tap approach; by seeking to reduce the level of contamination entering water sources, applying robust treatment barriers at the water treatment plants, and having monitoring programmes to help validate performance. A barrier is defined as any action, process, procedure, standard or asset put in place across the entire system, from source to tap, to help achieve water of sufficient quality and quantity.

Source Risk Assessment

The DWSP approach involves assessing a comprehensive range of hazardous events that could potentially occur in a drinking water supply. Where a hazardous event occurs, it can lead to the presence / manifestation of a hazard (e.g. the runoff of fertiliser to a river or leaking septic tank). The risk assessment of DWSP hazardous events involves determining the potential impact (i.e. severity) and likelihood (i.e. probability) of a hazardous event occurring and reaching drinking water. 

Uisce Éireann is developing semi-quantitative methodologies to risk assess drinking water sources, and carry out site specific Source and Sanitary Surveys to verify the risks on the ground. We are using the source-pathway-receptor (SPR) concept which requires an understanding of the pathways that contaminants might travel. These pathways differ depending on whether surface water or groundwater are the receptor and the characteristics of environmental components, such as soils, subsoils and geology. The impact on the receptor is also influenced by the level of dilution. Existing national scale catchment related datasets published by the Environmental Protection Agency (EPA) and Geological Survey Ireland (GSI) are being utilised.

Catchment Action Plans

The DWSP source risk assessments will inform the required catchment actions that will prevent or mitigate the likelihood of the hazardous events from occurring. The evidence-based approach to risk assessment will enable more informed decision making and prioritisation of risks to target the implementation of “the right measures in the right place”. 

Drinking water catchment action plans have to be completed for all sources by July 2027. These include the identification of the main risks to source water quality and the actions required to address those risks and identification of responsible stakeholders. The plans will be developed in collaboration with the relevant stakeholders, who share the common goal of reducing the risk of contamination of our drinking water sources.