HOMEOWNERS in Cork, Galway, Donegal and Kerry will have the most septic tank inspections from the summer.
The Environmental Protection Agency (EPA) says tanks in these counties will be targeted because groundwater is most at risk of pollution due to soil conditions and the sheer number of domestic waste-water systems.
The EPA's national inspection plan says 30 local authority inspectors will examine 1,000 tanks across the country every year – or one in every 500 – and those that are not operating correctly will have to be repaired or upgraded.
The introduction of an inspection regime comes after the European Court of Justice ruled Ireland had failed to protect water sources in contravention of EU rules.
In December, it issued fines totalling €2.6m.
Environment Minister Phil Hogan said complying with the ruling was a "high priority" of the Government, following years of inaction.
"This is a serious problem that I inherited and, unlike the previous administration, I prioritised bringing forward the necessary legislation to help solve the problem," he said.
Grants would be available to households whose systems needed to be repaired or upgraded, to a maximum of €4,000, he added.
There are some 500,000 septic tanks across the State which process waste water. If the water is not properly treated, it can pollute groundwater and pose risks to human health.
Homeowners had until February 1 to register their tanks, and 410,000 (82pc) have done so. The remaining 90,000 houses will be targeted for inspection. The inspection plan says that most inspections will be carried out in areas of high risk.
Almost one in 10 (99) will be conducted in Cork, followed by 98 in Galway, 80 in Donegal and 57 in Kerry. The lowest number of inspections will be in Carlow (12), Westmeath (14) and Dublin (15).
Homeowners will be given 10 days' notice and tanks will be checked to see if they are working properly.
The owner will be notified about the findings within 21 days, and if the system is deemed to pose a risk to public health or the environment, an advisory notice setting out the works to be carried out will be issued within another 21 days.
In disputed cases, a re-inspection can be carried out at a cost of €20.
The EPA said the aim of the inspection regime was to ensure that systems were working effectively and that risks to the environment were eliminated.
A public information campaign is expected to begin next month, with inspections due from July. The plan will be reviewed next year, and may lead to an increase in the number of inspections.