Half of septic tanks inspected last year failed to meet adequate standards, according to the Environmental Protection Agency.
In a report published today, the agency warned that homeowners need to take action to protect themselves, their neighbours and their families from risks posed by septic tanks.
There were 544 failure advisory notices issued in 2016, an increase of 11.5% on the previous year.
Local authorities, who carry out the inspections, can prosecute a homeowner if they fail to comply with the advisory notice.
One prosecution is pending against a homeowner in Co Louth following an inspection last year.
The highest number of advisory notices issued last year was in Co Wexford where 80 householders were issued with notices, followed by Cork at 68.
The lowest number was in Sligo, where no notices were issued.
The EPA said septic tank failures were mainly due to a lack of proper operation and maintenance.
It warned that the failure by homeowners to maintain and operate a septic tank system adequately can pose a health and environmental risk through the pollution of private drinking wells or water courses.
Programme Manager of the EPA's Office of Environmental Enforcement Darragh Page said: "There are simple steps that homeowners can take to ensure their system is managed properly and will pass an inspection.
"These include: having the sludge emptied from the tank on a regular basis, using a permitted contractor and retaining the receipt and, if the homeowner has a package treatment system, having it regularly serviced and keeping a record of servicing."
The Irish Farmers' Association called on the Department of Local Government and the EPA to establish a ring-fenced budget to address septic tank failure following publication of the report.
IFA Environment Chairman Thomas Cooney said: "The results show no improvement on previous years, demonstrating that the current procedure is not working".