The samples being taken at the old waterworks in Terryland in Galway city have been clear of contamination for the last two days, it emerged yesterday.
But the Health Service Executive (HSE) and Galway City Council have stressed that the public must continue boiling tap water and maintain stringent hygiene practices for some time yet.
The clear tests for cryptosporidium is good news for beleaguered city council officials who have been conducting tests several times a day at a cost of €25,000 a week. However an end to the water crisis, now entering its fourth week, is still some months off.
"There has been no levels of cryptosporidium for the last two days. The levels have been going down for some time but this is the first time they have been clear since this began," said city council director of infrastructure services Ciarán Hayes. "People should still boil the water. It is the HSE who will lift the boil notice."
The HSE West has stressed that it will cancel the boil notice only when there is a marked decline in notifications of human cases; when there are consistently low levels of the parasite in the treated public water supply and when there is an effective treatment system to remove the bug from the water.
So far there is no decline in the number of confirmed human cases. Last night the latest figure had increased to 173 from 155 on Monday.
At Monday night's council meeting, Mr Hayes said it would take until September before additional water from the Tuam treatment plant could be used in Galway city. The old plant at Terryland is to be phased out and a new treatment facility put in its place. This would take between nine months and a year.
The second treatment plant at Terryland, which was built about 15 years ago, has produced no positive tests for the bug. It is to be upgraded with an ultraviolet system and an ultrafiltration treatment system. Mr Hayes said it would be a matter of months before these two systems could be in place.
A special meeting has been organised for next Wednesday to further brief city councillors about the water crisis. Councillors are demanding an updated report from the city and county councils, including the contradictory evidence of water testing done by media outlets.
They want an updated report from the HSE that includes implications of lead content in the city water supply and all reports from the Environmental Protection Agency.