A water restriction means that people are advised not to use the water for drinking and are advised to use an alternative source of water, such as bottled water, or tankered water which must be boiled to make it safe before consuming.
For example, in Bailieborough, Cavan, elevated levels of manganese in the raw water source and issues at the water treatment plant resulted in 7,785 residents being advised not to consume the water for 11 days in 2019. An EPA audit at Bailieborough identified significant issues and many contributory factors which led to the need to place a restriction on the supply.
https://www.thejournal.ie/do-not-consume-water-notice-cavan-4934130-Dec2019/
The supply affected is Ballydermody, Waterford, which has been on a water restriction since 2013 due to high levels of nitrate.
Irish Water disputes that it has responsibility for this supply