Residents who were told not to use running water for nearly two days due to a contamination warning have been told they can use it again.
Bottled water was delivered to an estate in St Athan, Vale of Glamorgan, following a letter from water company Ancala on Thursday.
Ancala issued a statement apologising for the disruption and said the do not drink notice was precautionary.
But politician Jane Hutt said the situation was "unacceptable".
Ms Hutt, who is Member of the Senedd (MS) for Vale of Glamorgan, said: "The residents here need to be safe and secure with their water supply. We've got to have answers to what's happened from Ancala, a private water supplier.
"It must not happen again. I want to know why this happened on Thursday, what led to it, and to know what it was they were identifying in the water.
"It's been an unacceptable time. Three days of anxiety, uncertainty, not being able to get answers."
The company said the approval to start using the water again followed further tests on the water quality
Its latest letter said: "Water quality sampling has shown that the water at your property meets the regulatory prescribed values for wholesome water.
"Based on this you can now use and drink your tap water as normal."
Households were advised to run their water for about five minutes before using it.
Residents had earlier said they felt left "completely in the dark" after being told not to use their water, but with little further detail.
One of those was Holly Darch, who said she knew a lot of people who had been drinking the water until the initial letters arrived.
"Everyone was quite worried, not knowing what was in the water," she said. "No-one could tell us any answers."
Householders had also been warned not to give the water to pets or use the water for cooking or cleaning teeth.
In a statement on Saturday, Ancala said: "A routine water quality sample at the St Athan estate did not meet the high standards we require in line with regulatory requirements.
"As a precautionary measure a 'Do Not Drink' notice was issued."
It said the water had since been tested in a laboratory and met all standards for potable and wholesome water.