People in parts of Dublin and Wicklow have complained to Irish Water that their drinking water has been tasting and smelling "musty" and "earthy" over the past few weeks.
Irish Water said it is investigating the issue, but that initial tests indicate the water is safe to drink.
The utility said the taste and smell issues may be due to changes in the raw water characteristics, lake levels and seasonal changes at the Vartry Water Reservoir following a major supply outage last month.
It said it has received complaints from residential and business customers in Dublin city, the Dún Laoghaire-Rathdown area and north and east Wicklow.
As a result it said it carried out sampling and analysis of the water supplies in these areas.
In a statement, Irish Water said that "the water continues to fully meet chemical and microbiological regulatory standards and is safe to drink".
The utility said that following a major supply outage on 9 September reservoir levels have stabilised and reached full capacity, with network flows and pressure returning to normal operating conditions.
It is continuing to investigate the taste and smell issues, in partnership with Dún Laoghaire-Rathdown, Dublin City Council and Wicklow County Councils.
Regional Asset Operations Lead at Irish Water Kevin Love said: "We are currently investigating the source of the taste and odour issues and testing the water to determine the root cause.
"There may be a number of contributing factors and Irish Water are looking into possible changes in the raw water characteristics and lake levels that may be causing the complaints.
"The water treatment plant is operating in full compliance with drinking water regulatory parameters and will automatically shut down if specific online monitoring records a value greater than regulatory operating targets safeguarding public health.
"We have also carried out investigative and regulatory monitoring on the supply network to ensure the water quality meets regulatory compliance parameters and all samples have returned compliant results verifying the water is safe to drink."