Urban waste water treatment in Ireland

Waste water from our towns and cities requires appropriate treatment prior to being discharged into our lakes, rivers and seas. Uisce Éireann’s job is to make sure that waste water is treated correctly to protect our environment and our health, from waste water discharges. The EPA is the environmental regulator of Uisce Éireann. We issue and enforce authorisations for waste water discharges. You can find out more information regarding by navigating through this section.

Urban wastewater treatment in Ireland

What happens to our wastewater after it goes down the drain?

Illustrated overview of urban wastewater management, showing wastewater flowing from a community through underground sewers to a treatment plant, where harmful matter is removed, before treated wastewater is discharged safely into a river.

The purpose of wastewater treatment is to collect wastewater from our communities and remove pollutants so that the treated water can be safely released back into the environment. If wastewater is not properly treated, it can cause pollution and pose a risk to public health.

Uisce Éireann is responsible for ensuring that wastewater is treated to the standards set by the EPA to protect the environment and public health.

You can see the key environmental priorities that Uisce Éireann need to work on by visiting the urban waste water priority areas page .

See our latest Urban Wastewater Treatment report.

Check out the EPA’s Sewage Treatment Map to find out if there is a treatment plant near you.

How is wastewater treated?

Step by step diagram showing how wastewater is treated: wastewater enters a treatment plant, undergoes screening and settling followed by biological treatment to remove organic matter; in some cases, additional treatment stages remove nutrients and disinfect the water.

In 2024 most of Ireland’s wastewater was treated at plants designed to provide secondary treatment (59.7%) or secondary treatment with nutrient removal (38.7%).

The remainder was either conveyed to plants that provide a more basic form of treatment, known as primary treatment (1%) or was collected at areas that have no treatment plant and discharged directly into the water environment without any treatment (0.6%).

Storm water overflows

Sewers carry wastewater away from our homes and communities and convey it to treatment plants. Many sewers also collect rainwater runoff from impermeable surfaces such as roads. Sewers should have enough capacity to collect and retain wastewater during all normal weather conditions and all normal seasonal variations in wastewater load. In times of heavy rainfall, the rainwater runoff entering sewers can increase significantly. If rainfall is heavy or sustained enough the capacity of the treatment plant and sewer can be exceeded and the excess flow of wastewater is released through outlets referred to as storm water overflows.

Storm water overflows act as emergency safety valves and release the excess flow from the sewer directly into local waters, such as rivers. Without these releases there could be a greater risk to the environment and people’s health because the sewer and treatment plant could become inundated, and homes and streets flooded by sewage. Storm water overflows are common in many countries and the European Union recognises it is not possible in practice to construct wastewater works in such a way that all wastewater can be treated during situations such as unusually heavy rainfall. Discharges from storm water overflows are diluted by rainwater but may have the potential to cause short term pollution. In order to limit pollution, storm water overflows must meet certain national standards, for example they must not operate in dry weather.

Two-panel diagram of storm water overflows: under normal weather conditions, wastewater flows through sewers to a treatment plant; during heavy rainfall, excess water overwhelms the system and untreated wastewater overflows into a river.