A 'Do Not Consume Notice' issued last Friday remains in place for water supplies on Achill Island.
Everyone on the island, whether supplied by the Achill Public Water Supply Scheme or any of the group water schemes and parts of the adjacent mainland, is affected by the notice.
Irish Water is reminding people on the island that water should not be consumed or used to wash food.
An incident management team from Irish Water and Mayo County Council has been set up to manage the incident.
Tankers are in place at various locations on the island.
The recent influx of visitors due to more people holidaying at home this summer has meant an increased pressure on the island's water treatment plant.
According to Irish Water demand is up 50% on this time last year and it has led to higher levels of aluminium in the water, meaning it's not fit for consumption.
Anne Kilbane, Customer Services Operator at Achill Tourism said locals and tourists are working together to get through this situation.
A contingency plan is in place across the island with tankers in every village to supply water to the 2,500 residents and many visitors. Bottled water is being delivered to those who are considered vulnerable and not able to leave their homes.
Any vulnerable customers who have concerns can contact 1850 278 278.
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People are reminded to use their own containers when taking water from the tankers and to boil water before consumption as a precautionary measure.
People are also reminded not to use mains drinking water for bottle-fed babies.
The water is safe to use for hand washing and personal hygiene and customers should continue to follow public health advice on hand washing during the Covid-19 pandemic.
The Head of Asset Management with Irish Water, Sean Laffey told RTÉ's News at One: "This is not a boil water notice. This does not make it safe to drink. This water should not be made for drinks or washing food or brushing teeth."
He said, however, it can be used for bathing, flushing toilets and washing of utensils.
He said an unexpected consequence of the Covid-19 crisis is more people are holidaying at home and visiting places such as Achill.
The water treatment plant at Achill has a capacity for 3,000 people and for 98% of the year this works fine, he added.
East Cork water shortage as a result of burst main
Hundreds of households and businesses in East Cork are without water this evening following a burst water main serving Fota Island and the Great Island, including the town of Cobh.
Irish Water say they and Cork County Council are working to repair the break as soon as possible.
Water stored in reservoirs means the town of Cobh still has a water supply but there is a risk of interruptions and low pressure in the town and surrounding areas.