WaterCheck Ireland

Total Trihalomethanes (THMs) in Drinking Water in Ireland

Explore EPA Ireland monitoring records, listed exceedances and historical trends for Total Trihalomethanes (THMs) in public drinking-water supplies across Ireland.

THMs are by-products of water disinfection.

Latest monitoring year
2025
Page updated
September 2026
Data available
2021, 2022, 2023, 2024, 2025
1,139Monitoring results
1,139Samples
689Water supplies monitored
27EPA-listed exceedances

These are historical public-supply monitoring records, not a current water notice or a test of every household. Sampling locations can be outside the linked towns.

What do the latest results show?

The latest year is 2025. Results and listed exceedances are counted separately from their respective datasets.

  1. In 2025, 1,139 Total Trihalomethanes (THMs) monitoring results were recorded from 1,139 samples across 689 public water supplies.
  2. The separate EPA exceedance dataset lists 27 records across 24 schemes in 2025.
  3. There were 117 more monitoring results than in 2024 (11.4% more). This describes the volume of monitoring, not a change in water quality.

Total THM monitoring and the Irish standard

Recorded results for 2025, with official requirements shown separately.

Irish drinking-water requirement

100 µg/l

Sum of the four THMs specified in Schedule 1 Note 21.

This is separate guidance, not a test result for your own water. It does not reclassify historical records.

Official guidance checked 14 Sep 2026.

Monitoring coverage · 2025

Numeric measurements
935
EPA-listed exceedances
27
Water supplies monitored
689
First sample
27 Jan 2025
Latest sample
16 Dec 2025

These are historical records, not the current status of your water. EPA-listed exceedances come from a separate dataset.

The regulatory total covers chloroform, bromoform, dibromochloromethane and bromodichloromethane. The imported source provides a total, not four separate component measurements.

Monitoring measurement units are not verified, so these recorded values cannot be compared with the official standard. Units in the listed exceedance table are reproduced separately from that source.

How to read these results

Measurement coverage · 2021–2025

The imported monitoring records have no unit field. These are counts of recorded values, not concentrations or a comparison with the standard.

4,098 numeric records; 1,119 censored text records; 0 other text-only records; 2 records without a result value.

4,263 records have a non-empty text field, including records that also have a numeric value. This overlapping field count must not be added to the numeric total.

Result representation by year
YearNumericNon-empty text fieldCensored textOther text onlyNo result value
202180284322000
202281482919500
202375582327101
202479283222901
202593593620400

Across this period, 5,219 results from 5,219 samples cover 730 distinct water supplies. Sample dates run from 05 Jan 2021 to 16 Dec 2025.

20251,139 results · 27 listed exceedances · 689 schemes monitored
Monitoring results — independent scale
0569.51,139 1,022 2021 1,009 2022 1,027 2023 1,022 2024 1,139 2025
1,022
2021
1,009
2022
1,027
2023
1,022
2024
1,139
2025
EPA-listed exceedance records — independent scale
02448 48 2021 44 2022 46 2023 16 2024 27 2025
48
2021
44
2022
46
2023
16
2024
27
2025

These are record counts, not an official EPA compliance rate. The number and selection of samples and monitored schemes can change between years.

There were 117 more monitoring results than in 2024 (11.4% more). This describes the volume of monitoring, not a change in water quality.

Total Trihalomethanes (THMs) monitoring, 2021–2025
YearResultsSamplesSchemes monitoredListed exceedancesSchemes with listed exceedances
20211,0221,0226224840
20221,0091,0096084432
20231,0271,0276294636
20241,0221,0226291615
20251,1391,1396892724

EPA-listed Total Trihalomethanes (THMs) exceedances

181 listed records across 81 distinct schemes, 2021–2025. These are historical sample records, not a current assessment of each property in a supply zone.

Results and limits below are reproduced from the separate EPA exceedance dataset, with its own reported units. These units are not assigned to the wider monitoring dataset.

Listed exceedances by year and reported unit/limit pair
YearRecordsSchemesLowest listed resultHighest listed resultReported unitReported limit
20214840101190ug/l100
20224432100.3154.4ug/l100
20234636100.3190ug/l100
20241615101198ug/l100
20252724100.9228ug/l100
Show all 181 listed records 2021–2025 · newest first
All EPA-listed Total Trihalomethanes (THMs) exceedances in the reporting period
DateResultReported unitReported limitWater supply schemeScheme code
13 Oct 2025116ug/l100Limerick City Environs PWS1900PUB1032
13 Oct 2025118ug/l100Newcastle West PWS1900PUB1042
03 Oct 2025108ug/l100Cavanhill2100PUB1018
02 Oct 2025103.5ug/l100Navan-Mid Meath Kilcarn PWS2300PUB1051
22 Sep 2025124ug/l100Killadysert PWS0300PUB1008
15 Sep 2025103ug/l100Glengarriff0500PUB4208
12 Sep 2025101ug/l100West Clare Rws (Old Wtp)0300PUB1022
04 Sep 2025135ug/l100Three Mile House & Togan2400PUB2027
02 Sep 2025100.9ug/l100Ballany3200PUB1004
19 Aug 2025144ug/l100Cork Harbour & City0500PUB3401
18 Aug 2025148ug/l100Emyvale2400PUB1008
11 Aug 2025111ug/l100Killeshandra PWS0200PUB0113
07 Aug 2025112ug/l100Clones2400PUB1002
06 Aug 2025109.1ug/l100Barrow/Poulaphouca Blend1400PUB1070
01 Aug 2025101.9ug/l100Cavanhill2100PUB1018
29 Jul 2025104ug/l100Killadysert PWS0300PUB1008
18 Jul 2025144ug/l100GLENTIES-ARDARA0600PUB1070
07 Jul 2025108ug/l100LERWSS2400PUB1001
07 Jul 2025101ug/l100Drum2400PUB1007
06 Jun 2025102.1ug/l100Barrow Supply1400PUB1060
06 Jun 2025115.7ug/l100Navan-Mid Meath Kilcarn PWS2300PUB1051
21 May 2025106ug/l100Belturbet PWS0200PUB0108
02 May 2025128ug/l100Carraroe PWS1200PUB1009
23 Apr 2025228ug/l100Blacklion PWS0200PUB0109
09 Apr 2025125ug/l100Cleggan/Claddaghduff1200PUB1011
07 Apr 2025104ug/l100Foynes/Shannon Estuary PWS1900PUB1027
04 Apr 2025103ug/l100Ballymagroarty0600PUB1132
06 Sep 2024101ug/l100Ballyjamesduff RWSS0200PUB0106
20 Aug 2024198ug/l100Dunmore/Glenamaddy PWS1200PUB1018
20 Aug 2024155ug/l100Cahersiveen PWS 017H1300PUB1050
19 Aug 2024104ug/l100Cork Harbour & City0500PUB3401
09 Aug 2024110ug/l100LONGFORD CENTRAL2000PUB1010
22 Jul 2024144ug/l100GLENTIES-ARDARA0600PUB1070
10 Jun 2024145.8ug/l100Navan-Mid Meath Kilcarn PWS2300PUB1051
06 Jun 2024102.5ug/l100Barrow/Poulaphouca Blend1400PUB1070
17 May 2024121ug/l100West Clare Rws (New Wtp)0300PUB1066
13 May 2024124ug/l100Belturbet PWS0200PUB0108
13 May 2024101ug/l100North Roscommon Regional Water Supply Scheme2600PUB1012
07 May 2024108ug/l100LERWSS2400PUB1001
15 Apr 2024107ug/l100An Mhín Aird No. 1 PWS (060D)1300PUB1042
11 Apr 2024127.4ug/l100Trim2300PUB1009
03 Apr 2024101.5ug/l100Thurles Regional3700PUB1042
23 Feb 2024110ug/l100GLENTIES-ARDARA0600PUB1070
16 Oct 2023131ug/l100Killeshandra PWS0200PUB0113
09 Oct 2023101ug/l100Cavanhill2100PUB1018
05 Oct 2023103.7ug/l100Drumcondrath2300PUB1005
04 Oct 2023146.7ug/l100Navan-Mid Meath Kilcarn PWS2300PUB1051
03 Oct 2023139ug/l100Gort1200PUB1022
03 Oct 2023103.9ug/l100Fethard Regional Public Water Supply2900PUB0137
03 Oct 2023104.5ug/l100Thurles Regional3700PUB1042
25 Sep 2023121ug/l100Lyreacrompane RWSS 057E1300PUB1009
25 Sep 2023179ug/l100Kilgarvan PWS 046A1300PUB1059
22 Sep 2023128ug/l100West Clare Rws (Old Wtp)0300PUB1022
22 Sep 2023125ug/l100West Clare Rws (New Wtp)0300PUB1066
20 Sep 2023116.3ug/l100Clara/Ferbane PWS2500PUB1003
19 Sep 2023100.5ug/l100Kilkenny City (Radestown) PWS1500PUB1010
18 Sep 2023103ug/l100Limerick City Environs PWS1900PUB1032
11 Sep 2023132ug/l100Castletownbere0500PUB4205
07 Sep 2023106ug/l100Ballina - Lisglennon2200PUB1004
07 Sep 2023101ug/l100Ballina Town Mixed Supply2200PUB1008
06 Sep 2023104ug/l100FANAD EAST (SHANNAGH)0600PUB1043
05 Sep 2023107ug/l100LERWSS2400PUB1001
05 Sep 2023126ug/l100Three Mile House & Togan2400PUB2027
05 Sep 2023137ug/l100North East Regional PWS2600PUB1030
04 Sep 2023190ug/l100LETTERMACAWARD0600PUB1069
15 Aug 2023147.5ug/l100Kilkenny City (Radestown) PWS1500PUB1010
08 Aug 2023102ug/l100POLLAN DAM PUB0600PUB1020
02 Aug 2023109.3ug/l100Barrow/Poulaphouca Blend1400PUB1070
01 Aug 2023123ug/l100Shannon/Sixmilebridge RWSS0300PUB1040
01 Aug 2023138ug/l100Clones2400PUB1002
01 Aug 2023140ug/l100Emyvale2400PUB1008
01 Aug 2023119ug/l100SRRWSS - Killeglan2600PUB1004
01 Aug 2023105ug/l100Boyle Regional2600PUB1027
18 Jul 2023107.8ug/l100Kilkenny City (Radestown) PWS1500PUB1010
17 Jul 2023105ug/l100GLENTIES-ARDARA0600PUB1070
06 Jul 2023111ug/l100West Clare Rws (New Wtp)0300PUB1066
27 Jun 2023105ug/l100Limerick City Environs PWS1900PUB1032
27 Jun 2023106ug/l100Newcastle West PWS1900PUB1042
26 Jun 2023105ug/l100Carraroe PWS1200PUB1009
22 Jun 2023107.5ug/l100Cavanhill2100PUB1018
16 Jun 2023103ug/l100Belturbet PWS0200PUB0108
14 Jun 2023105.1ug/l100Barrow/Poulaphouca Blend1400PUB1070
12 Jun 2023101.6ug/l100Barrow Supply1400PUB1060
17 Apr 2023105ug/l100Lyreacrompane RWSS 057E1300PUB1009
17 Apr 2023169ug/l100Foynes/Shannon Estuary PWS1900PUB1027
17 Apr 2023111ug/l100SRRWSS - Killeglan2600PUB1004
11 Apr 2023102.2ug/l100Barrow Supply1400PUB1060
06 Apr 2023100.3ug/l100Trim2300PUB1009
04 Apr 2023101.1ug/l100Thurles Regional3700PUB1042
11 Oct 2022100.3ug/l100Cavan RWSS0200PUB0100
10 Oct 2022107ug/l100Foynes/Shannon Estuary PWS1900PUB1027
10 Oct 2022110ug/l100Newcastle West PWS1900PUB1042
04 Oct 2022104ug/l100Barrow/Poulaphouca Blend1400PUB1070
19 Sep 2022118ug/l100Cork Harbour & City0500PUB3401
19 Sep 2022102ug/l100Lyreacrompane RWSS 057E1300PUB1009
19 Sep 2022119ug/l100Aughacasla PWS 005D1300PUB1022
13 Sep 2022137ug/l100West Clare Rws (New Wtp)0300PUB1066
07 Sep 2022107ug/l100Killadysert PWS0300PUB1008
02 Sep 2022100.5ug/l100LETTERMACAWARD0600PUB1069
01 Sep 2022101ug/l100Loughrea - Knockanima PWS1200PUB1058
01 Sep 2022112.5ug/l100Trim2300PUB1009
01 Sep 2022106.3ug/l100Navan-Mid Meath Kilcarn PWS2300PUB1051
23 Aug 2022112ug/l100Cork Harbour & City0500PUB3401
22 Aug 2022126ug/l100Inisboffin PWS1200PUB1024
16 Aug 2022101ug/l100Kilkenny City (Radestown) PWS1500PUB1010
15 Aug 2022154.4ug/l100Cavan RWSS0200PUB0100
15 Aug 2022120.7ug/l100Blacklion PWS0200PUB0109
10 Aug 2022107ug/l100Kilsellagh Public Water Supply2700PUB2706
08 Aug 2022113ug/l100LONGFORD CENTRAL2000PUB1010
08 Aug 2022107ug/l100Clones2400PUB1002
02 Aug 2022109.7ug/l100Alt Raw & Meenreagh0600PUB3077
21 Jul 2022122ug/l100Inishere1200PUB1025
19 Jul 2022113ug/l100Kilkenny City (Radestown) PWS1500PUB1010
11 Jul 2022100.3ug/l100Barrow/Poulaphouca Blend1400PUB1070
11 Jul 2022111ug/l100Limerick City Environs PWS1900PUB1032
06 Jul 2022124ug/l100West Clare Rws (New Wtp)0300PUB1066
01 Jul 2022107.2ug/l100GLENTIES-ARDARA0600PUB1070
14 Jun 2022136ug/l100Ballymakerra0500PUB2303
14 Jun 2022103ug/l100Waterville PWS 075H1300PUB1057
13 Jun 2022116ug/l100LONGFORD CENTRAL2000PUB1010
17 May 2022102ug/l100Skibbereen Ballyhilty0500PUB4605
17 May 2022101ug/l100Kilkenny City (Radestown) PWS1500PUB1010
16 May 2022112ug/l100Spiddal Public Water Supply1200PUB1045
10 May 2022103ug/l100Barrow/Poulaphouca Blend1400PUB1070
09 May 2022102ug/l100Caragh Lake PWS 022A1300PUB1046
09 May 2022102ug/l100Limerick City Environs PWS1900PUB1032
09 May 2022103ug/l100North Roscommon Regional Water Supply Scheme2600PUB1012
03 May 2022123ug/l100West Clare Rws (Old Wtp)0300PUB1022
03 May 2022111ug/l100Ballina - Wherrew2200PUB1003
03 May 2022101ug/l100Ballina Town Mixed Supply2200PUB1008
12 Apr 2022118ug/l100LONGFORD CENTRAL2000PUB1010
04 Apr 2022101ug/l100Limerick City Environs PWS1900PUB1032
07 Mar 2022103ug/l100Limerick City Environs PWS1900PUB1032
14 Dec 2021106.1ug/l100Trim2300PUB1009
15 Nov 2021105.9ug/l100Milford Kerrykeel0600PUB1131
15 Nov 2021101ug/l100Foynes/Shannon Estuary PWS1900PUB1027
15 Nov 2021101ug/l100Newcastle West PWS1900PUB1042
09 Nov 2021154ug/l100Clare Island PWS2200PUB1030
08 Nov 2021116ug/l100Cork Harbour & City0500PUB3401
03 Nov 2021109ug/l100Bray PWS3400PUB1001
01 Nov 2021190ug/l100Wexford Town3300PUB1669
14 Oct 2021105ug/l100Gort1200PUB1022
13 Oct 2021108.7ug/l100Navan-Mid Meath Kilcarn PWS2300PUB1051
12 Oct 2021101ug/l100Poulaphouca Regional1400PUB1023
11 Oct 2021101ug/l100Skibbereen Ballyhilty0500PUB4605
07 Oct 2021110ug/l100Spiddal Public Water Supply1200PUB1045
06 Oct 2021108ug/l100Swinford PWS2200PUB1024
05 Oct 2021141ug/l100Galway City PWS1100PUB1001
24 Sep 2021121.9ug/l100LETTERMACAWARD0600PUB1069
21 Sep 2021177ug/l100Cahersiveen PWS 017H1300PUB1050
20 Sep 2021107ug/l100Listowel Regional Public Water Supply1300PUB1204
13 Sep 2021107ug/l100Castletownbere0500PUB4205
07 Sep 2021103ug/l100North Roscommon Regional Water Supply Scheme2600PUB1012
07 Sep 2021183ug/l100North East Regional PWS2600PUB1030
06 Sep 2021113ug/l100Loughrea - Knockanima PWS1200PUB1058
02 Sep 2021104.1ug/l100Drumcondrath2300PUB1005
02 Sep 2021106.7ug/l100Navan-Mid Meath Kilcarn PWS2300PUB1051
01 Sep 2021116ug/l100West Clare Rws (New Wtp)0300PUB1066
17 Aug 2021151ug/l100Kilkenny City (Radestown) PWS1500PUB1010
16 Aug 2021126.9ug/l100POLLAN DAM PUB0600PUB1020
10 Aug 2021108.1ug/l100Belturbet PWS0200PUB0108
05 Aug 2021107.97ug/l100Portumna PWS1200PUB1042
03 Aug 2021142ug/l100Greystones Windgates Templecarrig PWS3400PUB1003
03 Aug 2021104ug/l100WICKLOW REGIONAL SUPPLY3400PUB1005
20 Jul 2021150ug/l100Kilkenny City (Radestown) PWS1500PUB1010
10 Jun 2021108.7ug/l100LONGFORD CENTRAL2000PUB1010
02 Jun 2021140ug/l100Bray PWS3400PUB1001
02 Jun 2021140ug/l100Greystones Windgates Templecarrig PWS3400PUB1003
01 Jun 2021144.6ug/l100Navan Mid-Meath Liscarton PWS2300PUB1016
18 May 2021175ug/l100Kilkenny City (Radestown) PWS1500PUB1010
10 May 2021110.6ug/l100FANAD WEST (TULLYCONNELL)0600PUB1042
05 May 2021106.48ug/l100Loughrea - Knockanima PWS1200PUB1058
21 Apr 2021138ug/l100ENNISKERRY PUBLIC SUPPLY3400PUB1019
19 Apr 2021124ug/l100AUGHRIM ANNACURRA PUBLIC SUPPLY3400PUB1023
14 Apr 2021141ug/l100Bray PWS3400PUB1001
14 Apr 2021121ug/l100WICKLOW REGIONAL SUPPLY3400PUB1005
14 Apr 2021101ug/l100KILMACANOGUE PUBLIC SUPPLY3400PUB1009
14 Apr 2021111ug/l100BERRYFIELD LANE PUBLIC SUPPLY3400PUB1074
01 Apr 2021108.1ug/l100MILFORD PUB0600PUB1050
22 Mar 2021110ug/l100Limerick City Environs PWS1900PUB1032
09 Feb 2021116.1ug/l100GLENTIES-ARDARA0600PUB1070

Places with mapped Total Trihalomethanes (THMs) monitoring data

Explore existing place reports with mapped Water Supply Zones containing Total Trihalomethanes (THMs) monitoring records in 2021–2025.

95 published places have at least one qualifying mapped zone. The 20 largest are listed below by Census 2022 population, not by Total Trihalomethanes (THMs) levels.

Places can share the same Water Supply Zone. These links do not represent independent city measurements; sampling locations may be outside the named Built Up Area. National totals above count each source record once.

DublinDublinCorkCorkLimerickLimerickGalwayGalwayWaterfordWaterfordDroghedaLouthDundalkLouthSwordsDublinNavanMeathBrayWicklowEnnisClareCarlowCarlowKilkennyKilkennyNaasKildareTraleeKerryNewbridgeKildareBalbrigganDublinPortlaoiseLaoisAthloneWestmeathMullingarWestmeath

View all places — the complete published place directory.

Understanding the total THM parameter

The regulatory total covers chloroform, bromoform, dibromochloromethane and bromodichloromethane. The imported source provides a total, not four separate component measurements.

Current water information for your address

For current supply information, check your Eircode with Uisce Éireann. Follow the notice for your address: a Boil Water Notice and a Do Not Consume Notice have different instructions. This historical report does not recommend boiling as a treatment for chemical parameters.

Frequently asked questions

What does this Total Trihalomethanes (THMs) report cover?

5,219 monitoring records across 5 available monitoring year(s): 2021, 2022, 2023, 2024, 2025. The selected source is Trihalomethanes(Total). National totals come directly from EPA records, not a sum of towns.

What is the Irish drinking-water requirement for Total Trihalomethanes (THMs)?

100 µg/l. Sum of the four THMs specified in Schedule 1 Note 21.

Does the report show individual THM compounds?

No. Its source parameter is Trihalomethanes(Total). The reported total is not split into individual chemicals.

Can I compare the recorded Total Trihalomethanes (THMs) values with the standard?

Monitoring unit metadata have not been verified in this import. Numeric and censored records are counted separately; no concentration median, maximum or compliance rate is inferred from them. Listed records keep the units supplied by the separate EPA exceedance dataset.

Does a place link give the current Total Trihalomethanes (THMs) result at my address?

No. It identifies a place with a mapped supply and historical monitoring. It is not a test of every property. Check current Uisce Éireann supply information using your Eircode.

Sources and methodology

Monitoring data
EPA Ireland: drinking-water monitoring data: public-supply monitoring results and the separate listed exceedance records, 2021–2025.
Counting
Source records are counted once across schemes. A sample is identified by its scheme, sample ID and date. Listed exceedances are not inferred from numeric results.
Interpretation
Text and censored results are not converted to numbers. Missing values are not zero. Records do not establish conditions in an individual home or an official compliance rate.

Read the full methodologyView data sources