Urban Waste Water Treatment in Ireland

The objective of waste water treatment is to collect the waste water generated within our communities, remove polluting material, and then release the treated water safely back into the environment. 

Irish Water is the national water utility, responsible for the collection, treatment and discharge of urban waste water in Ireland.  The EPA is the environmental regulator of Irish Water.  We issue and enforce authorisations for waste water discharges.  You can find the location of sewage treatment plants in Ireland on the EPA's Sewage Treatment Map.   

The information below shows Irish Water’s progress with some of the key work it must carry out to improve waste water treatment and protect our environment from the adverse effects of waste water discharges.


Priority Areas where treatment needs to improve

There are deficiencies in many public sewers and waste water treatment plants, due to a legacy of underinvestment.  Consequently, waste water from some areas discharges into the environment without adequate treatment.  It will not be possible to fix all these problems in the short term, and therefore Ireland must ensure that the resources that are available are directed where they are most needed.  We have identified the priority urban areas where treatment must improve to resolve national environmental priorities.  You can find more information on these priorities in the Urban Waste Water Treatment Report

The number of priority areas where treatment needs to improve, decreased from 148 in 2017 to 132 in 2018 and down to 120 in 2019.  


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Raw Sewage Discharges to be Eliminated

Waste water must be treated before it is released back into the environment. Without such treatment the waste water we produce can pollute our waters and create a health risk. In mid-2019 untreated waste water, commonly referred to as raw sewage, from the equivalent of 77,000 people flowed into the environment from 36 towns and villages.

As part of their Capital Investment Programme, Irish Water planned to eliminate discharges of raw sewage from 31 of the 36 areas by the end of 2021. Irish Water will not meet this plan and it now expects that just 23 of these areas will be connected to treatment by the end of 2021. The remaining 13 areas will continue discharging raw sewage after 2021 and will be connected to treatment between 2022 and 2025.

14 areas that were discharging raw sewage have been connected to treatment plants since 2014.

Collection / sewerage systems



Ireland has a network of approximately 30,000 kilometers of sewers which collect waste water from our houses and businesses and convey it for treatment.  There is a significant shortage of knowledge on the capacity, condition and performance of many collection systems, for example the volume of waste water that escapes from these systems is not known. 

Irish Water is working to improve these knowledge gaps, and it plans to complete 44 detailed assessments, known as Drainage Area Plans, by 2021. 20 have been completed to date.


Storm Water Overflows


Storm water overflows are needed to relieve sewers of excess flows that arise during unusually heavy rainfall. They act as emergency safety valves releasing excess flow from the sewer directly into local waters. In the absence of such releases the treatment plant could be damaged, and homes and streets flooded by sewage.

Storm water overflows should only trigger in extreme rainfall and should not be used in normal conditions to compensate for a lack of sewer capacity. We require Irish Water to assess storm water overflows to determine if they meet certain criteria, for example they must not operate in dry weather.

Assessments of Certificate of Authorisation sites

Waste water discharges from over 550 small villages and estates with a population of less than 500 are subject to certificates of authorisation issued by the EPA; larger discharges require a licence.  The certificates require Irish Water to assess the waste water works serving these areas and identify any improvements needed to protect the environment from waste water discharges.  Irish Water plans to carry out this work on a phased basis, dealing with the higher risk areas first.

By the end of 2019, Irish Water plans to complete the following:

Carry out impact assessments at 63 areas identified as pressures on water bodies at risk of pollution.

‌Visit these 63 sites to identify any improvements needed to protect these water bodies from waste water discharges.



Ortho-P Compliance

The EPA sets limits in our licences for the amount of certain substances that are allowed in the effluent that is discharged from a licensed treatment plant.  These limits can change from plant to plant depending on legal requirements and on the water environment that the discharge is entering.  The graph below shows Irish Water's compliance with the limits for ortho-phosphate (Ortho-P) in their licences.  This is an important substance as it is a very significant cause of pollution in rivers and lakes.

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