Fingal County Council is awaiting the results of further tests today before deciding on whether to rescind a public alert issued to homes in the Swords area.
Tankers have been supplying drinking water to residents in Knocksedan Estate since Wednesday of last week after E.coli was discovered in the water system.
A broken pipe, thought to be the cause of the problem, has since been fixed, and tests carried out on Tuesday and yesterday were clear of E.coli contamination.
However, yesterday's tests revealed the presence of high levels of chlorine, which is commonly used to kill bacteria in waterworks.
Fingal County Council said that it would be preferable if the levels of chlorine were allowed to subside before residents used the supply.
Accordingly, residents of some 160 houses in the area have been advised not to use tap water for brushing teeth, preparing food or bathing children for at least another day.
The council said that it might not be possible to identify the exact source of the contamination. The priority was to inform people of the precautions they should take before using the water.
Any residents reporting feeling unwell have been advised to visit a doctor immediately.
The issue came to light when residents reported discoloration of their tap water on August 7th.
Following an initial investigation, water samples were taken for testing by the council's contracted central laboratory. The council said that it delivered its public alert to houses in the area on a number of occasions over the following days.
"As a precaution, all residents in Knocksedan were advised by leaflet to boil water for drinking," a spokeswoman said.
