Thousands of residents have been issued with an urgent warning not to drink their tap water at home.
Some 5,600 households in Ireland are affected by the notice which is due to higher levels of manganese in the water, making it unsafe to drink.
Manganese is a naturally occurring mineral that is found in some foods but it is toxic at high levels, reports Galway Beo.
Those who drink water with high levels of the substance over time could suffer problems with memory, attention and motor skills.
Small babies may also develop learning and behaviour problems if they drink water with too much manganese in it.
The HSE, Irish Water and Galway County Council issued the "do not consume" notice for residents in two Galway areas.
It means residents are advised against preparing food and drinking tap water, even if it has been boiled first.
More than 5,600 residents in Spiddal are directly impacted by the warning while another 256 are in Inis Oirr.
It means the public water quality is considerably compromised and a serious risk to health if drank.
The do not consume notice applies to all customers served by the Inishere PWS and as indicated in the red areas of the map.
It is also not a boil water notice, as boiling water that has elevated levels of manganese will not make it safe to drink.
Residents have been advised to use an alternative safe source of drinking water, such as bottled water when drinking, preparing drinks, cooking and preparing food.
This includes washing and preparing salads and other meals which are not cooked before eating.
The warning also advises against using tap water when brushing teeth, gargling and making ice.
Residents are also advised to throw away all existing ice cubes and filtered water in fridges and freezers.
Alternative water supplies will be stationed at Darley National School and White Horse Hotel, but this will have to be boiled before being used.
It is not yet known how long the consume notice will remain in place, but Irish Water will continue to liaise with the HSE and Galway County Council and lift the restriction as soon as possible.
Manganese is found in foods such as nuts, whole grains and leafy green vegetables and helps to process cholesterol, carbohydrates and protein.
It is the 12th most common element on the Earth's crust and has many health benefits, but is toxic at high levels.
