WaterCheck Ireland

Castlebar Tap Water Quality

EPA monitoring records for Water Supply Zones mapped to Castlebar contain 1,378 monitoring results across 71 parameters in 2025.

The separate EPA exceedance dataset contains 4 listed exceedance records across 3 parameters.

The most frequently listed were Colour (2), Coliform Bacteria (1) and E. coli (1).

These are historical monitoring records and do not confirm the current status of water at a specific address. Current notices are maintained by Uisce Éireann.

Latest monitoring year
2025
Page updated
September 2026
Water Supply Zone
Lough Mask RWSS
Geographic overlap
93.87%
1,378Monitoring results
71Parameters tested
4EPA-listed exceedances
68Samples

The Castlebar Built Up Area overlaps Lough Mask RWSS across approximately 93.87% of its land area.

Monitoring results apply to the Water Supply Zone as a whole and may include sampling locations outside Castlebar.

Selected monitoring data

Key drinking water parameters

Parameters are shown when measurements are available. Text-only and censored values remain unchanged in the detailed history.

Lead

2025 median1.5
2025 maximum2
Measurements in 20259

0 EPA-listed exceedances in 2025.

View parameter history

Individual numeric measurements from 2021–2025. Text-only and censored results are retained in the history JSON and are not plotted as numbers.

Open this chart to load the measurements.

Numeric resultEPA-listed exceedance

3 numeric measurements available; 27 text-only records retained in JSON.

Nitrate

2025 median1.945
2025 maximum2.81
Measurements in 20259

0 EPA-listed exceedances in 2025.

View parameter history

Individual numeric measurements from 2021–2025. Text-only and censored results are retained in the history JSON and are not plotted as numbers.

Open this chart to load the measurements.

Numeric resultEPA-listed exceedance

24 numeric measurements available; 4 text-only records retained in JSON.

E. coli

2025 median0 100ml
2025 maximum1 100ml
Measurements in 202566

1 EPA-listed exceedances in 2025.

View parameter history

Individual numeric measurements from 2021–2025. Text-only and censored results are retained in the history JSON and are not plotted as numbers.

Open this chart to load the measurements.

Numeric resultEPA-listed exceedance

249 numeric measurements available; 0 text-only records retained in JSON.

Coliform Bacteria

2025 median0 100ml
2025 maximum1 100ml
Measurements in 202566

1 EPA-listed exceedances in 2025.

View parameter history

Individual numeric measurements from 2021–2025. Text-only and censored results are retained in the history JSON and are not plotted as numbers.

Open this chart to load the measurements.

Numeric resultEPA-listed exceedance

249 numeric measurements available; 0 text-only records retained in JSON.

Fluoride

2025 median0.7
2025 maximum0.8
Measurements in 20259

0 EPA-listed exceedances in 2025.

View parameter history

Individual numeric measurements from 2021–2025. Text-only and censored results are retained in the history JSON and are not plotted as numbers.

Open this chart to load the measurements.

Numeric resultEPA-listed exceedance

28 numeric measurements available; 2 text-only records retained in JSON.

Iron

2025 median38.5 ug/l
2025 maximum129 ug/l
Measurements in 202566

0 EPA-listed exceedances in 2025.

View parameter history

Individual numeric measurements from 2021–2025. Text-only and censored results are retained in the history JSON and are not plotted as numbers.

Open this chart to load the measurements.

Numeric resultEPA-listed exceedance

236 numeric measurements available; 13 text-only records retained in JSON.

Arsenic

2025 median2
2025 maximum3
Measurements in 20259

0 EPA-listed exceedances in 2025.

View parameter history

Individual numeric measurements from 2021–2025. Text-only and censored results are retained in the history JSON and are not plotted as numbers.

Open this chart to load the measurements.

Numeric resultEPA-listed exceedance

6 numeric measurements available; 24 text-only records retained in JSON.

20251,378 results · 4 listed exceedances
Total results — independent scale
0 689 1,378 820 2021 974 2022 873 2023 850 2024 1,378 2025
Listed exceedances per 1,000 results — independent scale
0.000 5.727 11.455 2.439 2021 2.053 2022 11.455 2023 0.000 2024 2.903 2025

This is our descriptive frequency: listed exceedance records divided by result records, multiplied by 1,000. It is not an official EPA compliance rate. Differences in sampling volume and parameters tested affect comparisons. A missing denominator is shown as unavailable.

Monitoring history by year
YearResultsSamplesParametersListed exceedancesPer 1,000 results
2021820566522.439
2022974606522.053
202387354671011.455
2024850586700.000
20251,378687142.903

Year-to-year detail

2025 compared with 2024

Changes describe dataset volumes only. The comparison uses the previous available year.

Results
2024850
20251,378
+528
Listed exceedances
20240
20254
+4
Samples
202458
202568
+10
Parameters
202467
202571
+4

Parameters with EPA-listed exceedances

Values and limits are reproduced as reported. Different unit/limit pairs are shown separately.

Colour

2 listed exceedance records / 66 tests3.03%

Descriptive frequency of records, not an official compliance measure.

Highest listed result
27 Hazen
Reported limit
20 Hazen
Records with this unit/limit pair
2
Latest exceedance
01 Aug 2025

Coliform Bacteria

1 listed exceedance records / 66 tests1.52%

Descriptive frequency of records, not an official compliance measure.

Highest listed result
1 100ml
Reported limit
0 100ml
Records with this unit/limit pair
1
Latest exceedance
31 Jul 2025

E. coli

1 listed exceedance records / 66 tests1.52%

Descriptive frequency of records, not an official compliance measure.

Highest listed result
1 100ml
Reported limit
0 100ml
Records with this unit/limit pair
1
Latest exceedance
31 Jul 2025

Across the year

When were listed exceedances recorded?

Each point represents one listed exceedance record. Records on the same date remain separate.

Colour01 Aug 2025
21 HazenReported result
20 HazenReported limit
LOUGH MASK RWSSWater supply
JanFebMarAprMayJunJulAugSepOctNovDecColiform BacteriaColourE. coli01 Aug 2025 — Colour: 21 Hazen; reported limit 20; LOUGH MASK RWSS; sample 19122131 Jul 2025 — Coliform Bacteria: 1 100ml; reported limit 0; LOUGH MASK RWSS; sample 19096231 Jul 2025 — E. coli: 1 100ml; reported limit 0; LOUGH MASK RWSS; sample 19096213 Jun 2025 — Colour: 27 Hazen; reported limit 20; LOUGH MASK RWSS; sample 181875

4 listed exceedance records across 3 parameters in 2025.

Your mapped supply

Water supply

Every Water Supply Zone used for this page's headline figures is included. Geographic overlaps are reported separately and are not added together or weighted by population.

Lough Mask RWSS

93.87% geographic overlap with the Castlebar Built Up Area.

Technical mapping details
EDEN code
2200PUB1032
Local authority
Mayo
Page totals
Included
Spatial rank
1
Historical EPA scheme
Available
Latest monitoring year
2025

Detailed data

The complete parameter and listed exceedance tables for the reporting year.

71 parameter rows4 listed exceedance records68 samples
Show detailed data71 parameters · 4 exceedance records

Complete parameter index

All parameters in 2025

All parameters with test results or listed exceedance records in the latest reporting year
1,2-dichloroethane9018 Nov 20251
2,3,6-trichlorobenzoic acid9018 Nov 20251
2,4-D9018 Nov 20251
Acrylamide9018 Nov 20251
Aluminium54019 Dec 20251
Ammonium9018 Nov 20251
Antimony9018 Nov 20251
Arsenic9018 Nov 20251
Atrazine9018 Nov 20251
Bentazone9018 Nov 20251
Benzene9018 Nov 20251
Benzo(a)pyrene9018 Nov 20251
Bisphenol A7018 Nov 20251
Boron9018 Nov 20251
Bromate9018 Nov 20251
Cadmium9018 Nov 20251
Chlorfenvinphos9018 Nov 20251
Chloride9018 Nov 20251
Chromium9018 Nov 20251
Clopyralid9018 Nov 20251
Clostridium Perfringens9018 Nov 20251
Coliform Bacteria66119 Dec 20251
Colony Count @ 22°C57019 Dec 20251
Colour66219 Dec 20251
Conductivity66019 Dec 20251
Copper9018 Nov 20251
Cryptosporidium2012 Feb 20251
Cyanide9018 Nov 20251
Cypermethrin9018 Nov 20251
Dichlobenil9018 Nov 20251
Dichlorprop9018 Nov 20251
Diflufenican9018 Nov 20251
Diuron9018 Nov 20251
E. coli66119 Dec 20251
Enterococci66019 Dec 20251
Fluoride9018 Nov 20251
Free Chlorine66019 Dec 20251
Giardia2012 Feb 20251
Glyphosate9018 Nov 20251
Haloacetic acids (Sum of 5 HAAs)8018 Nov 20251
Iron66019 Dec 20251
Isoproturon9018 Nov 20251
Lead9018 Nov 20251
Linuron9018 Nov 20251
Manganese9018 Nov 20251
MCPA9018 Nov 20251
Mecoprop9018 Nov 20251
Mercury9018 Nov 20251
Metaldehyde9018 Nov 20251
Microcystin-LR5018 Nov 20251
Nickel9018 Nov 20251
Nitrate9018 Nov 20251
Nitrite (at tap)9018 Nov 20251
Odour58019 Dec 20251
PAH9018 Nov 20251
Pendimethalin9018 Nov 20251
Pesticides - Total9018 Nov 20251
pH66019 Dec 20251
Propyzamide9018 Nov 20251
Selenium9018 Nov 20251
Simazine9018 Nov 20251
Sodium9018 Nov 20251
Sulphate9018 Nov 20251
Sum of PFAS (sum of 20)8018 Nov 20251
Taste58019 Dec 20251
Tetrachloroethene & Trichloroethene9018 Nov 20251
Total Chlorine66019 Dec 20251
Total Organic Carbon9018 Nov 20251
Triclopyr9018 Nov 20251
Trihalomethanes(Total)9018 Nov 20251
Turbidity (at tap)66019 Dec 20251

Showing 71 of 71 parameters.

EPA exceedance dataset

Listed exceedances in 2025

Newest first. Sample IDs distinguish records that may otherwise look identical.

All listed exceedance records in the latest reporting year
DateParameterResultUnitReported limitWater supply / EDENSample ID
01 Aug 2025Colour21Hazen20LOUGH MASK RWSS
2200PUB1032		191221
31 Jul 2025Coliform Bacteria1100ml0LOUGH MASK RWSS
2200PUB1032		190962
31 Jul 2025E. coli1100ml0LOUGH MASK RWSS
2200PUB1032		190962
13 Jun 2025Colour27Hazen20LOUGH MASK RWSS
2200PUB1032		181875

Common questions

Frequently asked questions

Is Castlebar tap water safe to drink?

WaterCheck Ireland does not issue a current safe or unsafe verdict. This page presents historical monitoring data. Check Uisce Éireann for any current Boil Water or Do Not Consume notices affecting your address.

Can you drink tap water in Castlebar?

WaterCheck Ireland provides historical drinking-water monitoring data, not a current safe or unsafe verdict. For current Boil Water or Do Not Consume notices, check your Eircode with Uisce Éireann.

What is the tap water quality in Castlebar?

In 2025, monitoring data for the Water Supply Zone mapped to Castlebar included 1,378 results across 71 parameters. The separate EPA-listed exceedance dataset contains 4 records for those zones in 2025. These figures summarise historical records and are not a current safety verdict.

Who monitors drinking water quality in Castlebar?

The historical monitoring figures shown here come from drinking-water datasets published by the Environmental Protection Agency (EPA), Ireland. Uisce Éireann operates public water supplies and publishes current supply notices.

What is a Water Supply Zone?

A Water Supply Zone is a defined area supplied by a public drinking-water system. Monitoring records apply to the zone as a whole, so sampling locations can be outside the Census Built Up Area.

What does a listed exceedance mean?

It is a record published in the separate EPA exceedance dataset. WaterCheck Ireland reproduces those records and does not infer additional exceedances or turn the record count into a safety assessment.

How can I check current water notices for my Eircode?

Use your Eircode on the Uisce Éireann website to check current Boil Water and Do Not Consume notices. This page is based on historical monitoring data and is not a live notice service.

Explore nearby reports

Water Quality Near Castlebar

Nearest published Built Up Areas, ordered by straight-line distance between Census reference points.

WestportMayo · approximately 16.2 kmBallinaMayo · approximately 30.5 kmTuamGalway · approximately 47.6 kmGalwayGalway · approximately 65.5 kmOranmoreGalway · approximately 69.4 kmSligoSligo · approximately 70.9 km

Connected by mapped supply

Places sharing this Water Supply Zone

These published places share at least one Water Supply Zone used in this page's headline figures.

WestportLough Mask RWSS

How this page is made

Sources and methodology

Settlement
Census 2022 Built Up Area: Castlebar. Population refers to the whole Built Up Area.
Supply mapping
Uisce Éireann Water Supply Zone boundaries are matched geographically to the settlement.
Monitoring
EPA monitoring results and the separate listed exceedance dataset, 2021–2025.
Interpretation
Geographic overlap measures land area, not population served; monitoring applies across the full supply zone.

Read the full methodologyView data sources