Public water supplies

Northern Ireland Water is the public water supplier in Northern Ireland. The DWI investigates incidences where drinking water quality standards have been breached or compromised and also carries out an annual assessment of Northern Ireland Water.


You can view current and historical reports on the compliance with the drinking water quality standards using the link below:-

The following Drinking Water Quality tables provide detail of individual water supply zones where full compliance with the regulatory standards has not been met.

Monitoring of Public Water Supplies

NI Water must monitor all the water it supplies that is intended for human consumption. The annual sampling frequencies are dictated by The Water Supply (Water Quality) Regulations (Northern Ireland) 2017 (the Regulations). This monitoring programme must be kept under review and updated or reconfirmed at least every five years. DWI regulates NI Water’s implementation of its monitoring programme, and assesses the drinking water quality to ensure the provision of safe clean drinking water.

Flexibility is provided in the Regulations for NI Water to deviate from the monitoring requirements by increasing reducing the sampling frequencies or adding / removing parameters monitored where set criteria are met. Any proposed deviations must be based on historical monitoring data and be subject to a risk assessment of the treatment works and its related water supply system. To remove a parameter or reduce the sampling frequency, the risk assessment must confirm that there will be no likely deterioration of the water quality and the Department must consent to the deviations by issuing a notice to NI Water.

Based on evidence provided by NI Water, a Notice of Decision not to monitor radioactivity in a number of water supply areas was issued by the Department to NI Water in December 2022. This Notice is for a period of five years. The Notice may be withdrawn in the event of any change in risk.

Enforcement Policy

If Northern Ireland Water fails to meet the required standards, the DWI may take enforcement action as detailed in the Environment, Marine and Fisheries Group Enforcement Policy:-

You can view historical and current Enforcement Action taken against NI Water using the links below. These may be in the form of:

Prosecutions are taken forward in the name of the Chief Inspector where there is reliable evidence that an offence has been committed, where the company does not have a defence that it took all reasonable steps and exercised all due diligence, and when such a prosecution is regarded as being in the public interest by the Public Prosecution Service. The offences for which the Inspectorate can initiate proceedings are criminal offences.

Prosecutions taken forward by the Public Prosecution Service on behalf of the Drinking Water Inspectorate can be viewed here.

The Drinking Water Inspectorate may also issue Warning Letters where it is satisfied that a regulatory breach has occurred. The company is issued with a warning that any further repeat events of this nature could result in further sanctions, including enforcement or prosecution. Warning letters issued by the Drinking Water Inspectorate can be viewed here.


The following legislation implements the requirements set out in the European Drinking Water Directive (98/83/EC), the amending Directive (EU) 2015/1787 which revised the monitoring and analysis requirements in Annex II and Annex III of Directive (98/83/EC), and Directive 2013/51/Euratom in respect of public drinking water supplies:

The Water Supply (Water Quality) Regulations (Northern Ireland) 2017

DWI also has regulatory responsibilities for drinking water quality supplied, via a domestic distribution, to the public in premises such as schools, hospitals and restaurants under:

Guidance on the Water Supply (Water Quality) Regulations (NI) 2017

Other Guidance

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