Environment

Which areas have been exposed to ‘potentially dangerous’ chemicals in water?

Chlorine helps ensure safe drinking water, but organic matter can react with the chlorine to form trihalomethanes

The State water authority has been working for several years to eliminate trihalomethanes, known as THMs, from drinking water supplies. Photograph: iStock
The State water authority has been working for several years to eliminate trihalomethanes, known as THMs, from drinking water supplies. Photograph: iStock
Mon Feb 12 2024 - 16:18

Uisce Éireann is taking advice on whether it needs to warn more than 220,000 consumers that their drinking water contains a level of toxic chemicals called trihalomethanes (THMs) in excess of that permitted under European Union limits, The Irish Times reported on Monday.

The places affected are listed and mapped below.

The State water authority has been working for several years to eliminate trihalomethanes, known as THMs, from drinking water supplies. These were the subject of a European Court of Justice (ECJ) finding against Ireland in recent weeks.

[ What are THMs and what risks do they pose in Irish water? ]

[ Uisce Éireann ‘taking advice’ on warnings to more than 220,000 people about presence of toxic chemicals ]

The problem with THMs in Irish drinking water supplies has been known about for many years. The use of chlorine helps ensure safe drinking water, but when organic matter is present it can react with the chlorine to form THMs.

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This is often the case in Ireland, as most of our drinking water comes from surface-water sources, such as rivers, lakes and streams, that often have high levels of vegetation or organic matter.

Uisce Éireann has said it took advice from the Health Service Executive (HSE) concerning THMs and drinking water. It said the advice was that the “benefits of using chlorine to treat our drinking water are much greater than any possible health risk from THMs”.

In its recent decision against Ireland, the ECJ said: “In the present case, the failure to comply with the parametric value set for THMs constitutes, by definition, a potential danger to human health.”

Hover over the circles to see affected populations

Affected areas

Co Clare: West Clare RWS

Co Cork: Mitchelstown North, Castletownbere

Co Donegal: Lettermacaward, Glenties-Ardara, Milford

Co Kerry: Cahersiveen, Caragh Lake, Listowel Regional Public Water Supply, Kilgarvan, Lyreacrompane

Co Kilkenny: Kilkenny City (Radestown) WS

Co Limerick: Limerick City Environs

Co Longford: Longford Central

Co Louth: Cavanhill

Co Mayo: Clare Island

Co Meath: Drumcondrath, Navan

Co Monaghan: Clones

Co Offaly: Clara/Ferbane

Co Roscommon: North East Regional

Co Tipperary: Nenagh Regional, Thurles Regional

Co Wicklow: Aughrim/Annacurra

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