Operational problems at the main water treatment works serving the Irish capital triggered a boil notice affecting over 600,000 people across the greater Dublin area last week.
An inspection by the Environmental Protection Agency (EPA) after the incident at the Leixlip water treatment plan revealed a technical malfunction which meant the barrier against cryptosporidium and giardia parasites was compromised for 14 hours. The boil notices lasted four days and covered much of the capital and its hinterland.
The EPA said the incident resulted in a "significant risk to the safety of the water supply", and highlighted that staff failed to respond to multiple alarms.
Meanwhile, in a separate development the publicly-owned company announced it would plead guilty to a prosecution brought by the EPA over failure to verify that levels of trihalomethanes in drinking water supplies in County Cork were not excessive.