1,700 small private supplies are registered with local authorities, but the Environmental Protection Agency says many more are not included in official records.
The environmental watchdog says new laws are needed to make sure all private drinking water supplies are properly registered.
The EPA says many private wells are not registered - despite supplying water to schools, nursing homes and sports clubs.
The fact they they are not registered means they can't be monitored.
1,700 small private supplies are registered with local authorities, but the Environmental Protection Agency says many more are not included in official records.
Noel Byrne, from the EPA's Drinking Water and Waste Water Enforcement team, says current laws need to be updated.

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