Some 40 per cent of public drinking water supplies monitored by the Environmental Protection Agency (EPA) last year were not meeting required standards to protect against cryptosporidium contamination, according to the EPA.
A workshop on cryptosporidium at the Institute of Technology in Sligo last week heard EPA inspector Darragh Page explain that because turbidity levels in the water at these plants in 2006 were above recommended limits, they were at risk of cryptosporidium contamination.
Even more serious problems were uncovered at 65 other treatment plants to which the Minister for the Environment has now allocated funds to upgrade or replace.
Most of these are in counties Kerry, Galway and Wicklow.
Mr Page said the EPA had monitored some 200 water supplies - from a total of about 950 supplies in the State.
"Sixty-five supplies - or 64 now that Galway has a new treatment plan - were found to have inadequate treatment. There was no barrier, so if cryptosporidium gets into the river or lake, it goes straight through into the water supply," Mr Page told The Irish Times.
Of the remaining plants monitored, 40 per cent were found to be at risk of cryptosporidium contamination because of turbidity exceedances - compared with 35 per cent in 2005 - and 20 per cent were at "high risk".
Contamination would depend on a number of factors - the pathogen being present and the treatment being inadequate at the same time.
He said the management of water treatment plants - the responsibility of local authorities - was crucial.
"There are a number of treatment plants trying to push through too much water, more than they were intended for," he added.
More than 130 delegates, mostly from local authorities and the Health Service Executive (HSE), attended the one-day workshop at the Institute of Technology in Sligo last Wednesday, which was jointly hosted by the John Hopkins Bloomberg School of Public Health in Baltimore, in the US.
Researchers from Sligo and the Baltimore college are currently working on a joint research project into cryptosporidium and other pathogens.
Dr Thaddeus Graczyk from the John Hopkins Bloomberg School of Public Health, in collaboration with Sligo IT researchers, has been conducting a study of the treatment of waste water at a number of plants in the west of Ireland.
Waste water goes through a process of sludge activation and he said they found that this process was generally efficient in removing human pathogens - an average of 70-80 per cent was removed.
However, 20 per cent of pathogens, which include cryptosporidium, remain in the sludge.
"This sludge is very frequently spread on fields as fertiliser after being stored for a period of six months," Dr Graczyk said.
The next part of the study is to sample the sludge after the six-month period.
If cryptosporidium and other pathogens are still in the sludge when it is spread on land, it is then likely that when it rains these will be washed off the land and into lakes and rivers - the sources of drinking water, Dr Graczyk said.
"This is the key question - how the spreading of sludge affects drinking water quality," he said. He pointed out that this practice of spreading sludge on land was widespread in Europe and the US.
He said he believed the outbreak of cryptosporidiosis in Galway earlier this year was "a wake-up call" and the issue was now being addressed with greater urgency.
Researchers at the Institute of Technology in Sligo are also about to begin EPA-funded research into the efficiency of water treatment plants in Sligo in the removal of human pathogens.