A boil water notice remains in place for most large towns in Co Mayo.
Restrictions were introduced at the beginning of the month, after tests at the Lough Mask water treatment plant revealed the presence of cryptosporidium.
A full audit of the treatment plant was carried out by inspectors from the Environmental Protection Agency last week.
The findings were considered by the Health Service Executive, Irish Water and Mayo County Council over the weekend.
Irish Water said the audit found improvements to filtration management at the plant, since the last EPA inspection in May 2015, when an audit found there was a risk of cryptosporidium entering the supply, if it was present in untreated water.
At the time, the EPA said there were significant issues in the performance of some filters at the plant, which required urgent attention.
The latest audit has not yet been made public by the EPA but Irish Water says all recommendations in it are being implemented.
Ongoing sampling of the water supply has not found any further presence of cryptosporidium but the boil notice remains in place.
Over 46,000 people affected by the restrictions are being told to boil water before it is used for drinking, food preparation, making ice or brushing teeth.
The notice applies to the public supply in and around the towns of Ballinrobe, Westport, Castlebar, Claremorris, Ballyhaunis and Knock.
Almost 50 Group Water Schemes are also subject to the warning.