There are now almost half a million domestic waste-water treatment systems registered in Ireland, according to the Central Statistics Office (CSO).
These systems, which usually consist of septic tanks, work by collecting, treating and discharging waste water from houses that are not connected to the public sewer network.
The CSO said that the number of registered systems increased by 1.2% to 487,423 in 2022.
There was an increase in every local authority with Wexford and Leitrim recording the highest annual increase of approximately 2% each.
Homeowners owned 97% or just over 473,000 of all registered waste-water treatment systems.
Public authorities accounted for 1.5% and other non-domestic owners accounted for the remaining 1.4%.
In Co. Longford, public authorities accounted for 4% of all owners in 2022, whereas in Co. Kildare they only accounted for 0.1%
Treatment systems
Seven counties accounted for just over half of all individual waste-water treatment systems in the country, according to the CSO.
In 2022, with 55,700 registered domestic waste-water treatment systems, Co. Cork had the highest proportion of systems at 11% followed by counties Galway with 43,061 (9%) and Kerry with 34,170 (7%).
Next were counties Donegal, Mayo and Tipperary at 6% each and Wexford at 5%.
Co. Cork accounted for 11% of all new registrations in 2022 followed by counties Galway and Donegal with 8% each.
Dublin was the county with the lowest number of systems at 6,429.
Under government legislation, all household connected to domestic waste-water treatment systems are required to register them.
It is an offence for a householder not to register and, if convicted, the penalty is a fine of up to €5,000.
Registration was introduced to address a European Court of Justice ruling against Ireland in October 2009.
The legislation aims to protect ground and surface water quality, particularly drinking water sources, from risks posed by faulty systems.