How Uisce Éireann Are Addressing THM Risks in Ireland

THM risks

How Uisce Éireann Are Addressing THM Risks in Ireland

4 months ago, data from the Environmental Protection Agency (EPA) reported public drinking water for nearly 240,000 people across Ireland contained unsafe THM levels. But what is being done to address THM risks in Ireland? 


A Summary of THM contamination in Ireland  

Trihalomethanes (THMs) are a by-product of chlorine water disinfection. Chlorine interaction with organic matter in water forms THMs. There are links between THM exposure and cell damage, DNA damage, and DNA mutations, a potential precursor to cancer. At the start of 2024, European Courts ruled that THM levels were above the acceptable threshold in many parts of Ireland. As a result, roughly 5% of the population had access to unsafe drinking water.  


Uisce Éireann’s Response to THM Risks in Ireland 

The Remedial Action List (RAL) is an EPA register of public water supplies needing corrective action. The latest RAL includes areas at risk of THM exposure. The identification of THM risks has led to a response from Uisce Éireann. However, stopping chlorination to prevent THM development is not an option. The World Health Organisation (WHO) states that “adequate disinfection should never be compromised to control THMs.” As a result, Uisce Éireann has developed alternative remedial actions to reduce THM risks. 


Mitigating THM Risks By Water Monitoring

One way Uisce Éireann is fighting the THM problem is through intensified monitoring efforts. When THM levels above the EU’s acceptable limit (100µg/L) are detected, Uisce Éireann notifies the EPA and consults with the Health Service Executive (HSE). Uisce Éireann’s enhanced monitoring programme has identified several additional sites where THM risks exist. Once risk areas are detected, an action plan is developed to address these risks. 


Uisce Éireann’s Action Plans to Reduce THM Levels 

The latest EPA RAL highlights areas at risk of high THM levels and actions being taken by Uisce Éireann to mitigate these risks. Such actions include: 

Use of Granular Activated Carbon (GAC) filtration. When water flows through GAC filters, any THMs present in the water stick to the surface of the carbon particles because of their unique structure and the way they attract specific molecules. This process is called adsorption and can remove THMs from water.

Replacing Dissolved Air Flotation Filtration (DAFF) with Coagulation/Flocculation/Clarification (CFC). DAFF creates tiny bubbles that attach to particles in the water, causing them to float to the surface for removal. On the other hand, CFC involves the addition of coagulants to make small particles clump together into larger ones (flocs) that can then be removed. CFC is better at removing organic compounds, including THMs. 

Introduction of other measures, including:

  • Development of new groundwater sources.
  • Connection of the water system to a better treatment plant.
  • Optimisation of network/reservoir cleaning. 


The Results of Uisce Éireann’s Efforts 

As a result of Uisce Éireann’s quick response, the majority of public water schemes identified by the EU concerning THM levels have now been addressed, with just 5 of the original 74 schemes remaining. Projects are underway at all 5 remaining locations to address the issues. To date, a Do Not Drink notice has not been imposed on any public water supply due to THM exceedances. 


Conclusion for Addressing THM risks in Ireland

Despite recent THM concerns, Uisce Éireann is working hard to safeguard our health through action plans. Uisce Éireann’s upscaled monitoring programme is also vital to fighting the THM problem. Checking water quality regularly makes sure it is safe to drink. Here at Southern Scientific Services, we offer accredited water quality testing to ensure water is free from toxic contaminants, including THMs. 


Follow the link to learn more about our THM in water test today!

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