Well water treatment in Co. Mayo

Private wells in Co. Mayo

Far more Mayo homes are on a group scheme than on a well. The 2022 Census counted 16,669 households on a public or private group water scheme, 32.1% of homes, against 2,892 on a private well or other private supply, 5.6%. Group schemes serve 48.2% of homes around Swinford, 38.1% around Belmullet, 35.4% around Claremorris and 35.1% around Westport. Private supplies are most common around Westport, at 9.8%.

This page is for the homes on their own well. Nobody monitors a household well for you. It's classed as an exempted supply, so testing and treating it is down to the owner, and the EPA advises a test at least once a year. Every system we fit in Mayo starts with a lab report.

What's usually in a Mayo well

Hard water on the limestone

Large parts of Mayo, around Ballina, Swinford, Castlebar, Claremorris and Cong, sit on limestone, and the Geological Survey of Ireland (GSI) measured mostly hard to very hard water on it. A group scheme spring at Lissatava in the Cong-Robe area ranged from 122 to 452 mg/L, Ballyvary from 122 to 444 mg/L and Ballina to Crossmolina from 316 to 380 mg/L.

Iron, manganese and sulphur

Between Ballina and Crossmolina, the GSI says high iron and sulphur are reported to be common, with iron reaching 1.8 mg/L in one sample and a slightly sulphurous smell in one well north of Ballina. A sandstone sample in the Foxford area had iron at 5.9 mg/L and manganese at 0.8 mg/L, and samples around Kilkelly and Charlestown showed iron up to 1 mg/L. You see iron as orange or brown staining, manganese as black specks, and sulphur as a rotten-egg smell.

Bacteria

Around Claremorris and Ballyhaunis, the karst limestone that runs up from east Galway carries groundwater fast through open channels, so whatever reaches the ground near a well, from a septic tank or a farmyard, can get into it quickly. Group schemes have had trouble too: Curraunboy and Robeen failed the E. coli standard in 2023 and 2024, and Curraunboy failed again in 2025. Nationally, the EPA estimates at least 30% of private wells are contaminated by E. coli. See bacteria in well water.

Mixed in the west, soft on granite

Erris and the Nephin Beg range are mostly quartzite, gneiss and schist, and water there varies widely, from 46 to 412 mg/L. Granite water in the Foxford area was soft, at 66 mg/L. On soft water a softener is often not needed.

What we usually fit in Mayo

Most Mayo wells on the limestone need the line below, in this order, with stages left out if the report doesn't call for them:

1. Sediment filter to protect everything after it.
2. Iron and manganese filter, which also deals with a sulphur smell and stops iron fouling the softener.
3. Water softener for the hard limestone water. On soft western or granite water it's often not needed.
4. UV disinfection if the report shows E. coli or coliforms, fitted last on the main line so the water reaching the lamp is clear.
5. Reverse osmosis at the kitchen tap for drinking water, if you want it.

Our own plumbers fit and service well systems across Mayo. For a rough idea of prices before you have a report, see what well water treatment costs.

The well grant in Mayo

Mayo County Council administers the domestic well grant in its area as the housing authority. Under the national terms the house must not be able to connect to Uisce Éireann or a group scheme, which matters in a county with so many schemes. Check the council's conditions before any work starts, then bring it your lab report and our itemised quote. We'll tell you which tests to ask the lab for: iron, manganese, hardness, pH, nitrate, E. coli and coliforms at the very least.