A boil water notice issued on 5 February for customers supplied by the Lough Talt Public Water Supply in Co Sligo and part of Co Mayo, following the detection of cryptosporidium, has been extended.
Irish Water has said a two-week testing and sampling programme has concluded with two more positive detections of the parasite.
Following a meeting with the Health Service Executive yesterday, a further two weeks of sampling and testing was agreed and the results will be reviewed.
The boil water notice affects about 13,000 people in the south and west Sligo area, and in the area supplied by the Ogham Group Water Scheme in Co Mayo.
However, according to the HSE, there have been no cases of associated illness reported in the community to date.
A planning application lodged by Irish Water in 2015 for a new treatment plant at Lough Talt was refused for reasons of protected habitat at the lake.
As the situation continues, Irish Water says it is urgently progressing with an alternative design proposal and will be in consultation with the relevant stakeholders regarding this detailed option over the next few weeks.