The EPA has highlighted serious issues at 50 treatment plants.
The water supply to over one million people is vulnerable to failure according to the Environmental Protection Agency.
It says Irish Water must urgently address more than 50 treatment plants which are at risk.
They include the Abbeyleix supply, which has inadequate treatment for cyrptospiridium, and the Clara-Ferbane supply, which has elevated levels of trihalomethanes.
It's also warning it will take Irish Water over 60 years to replace lead piping if the current pace is continued.
According to the HSE, lead poisoning can lead to kidney problems, high blood pressure and developmental issues in children.
Programme Manager at the EPA Andy Fanning says targets for the next few years should be upped:
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