Audits were carried out by the environmental regulator after the discovery of cryptosporidium in the water supply of Ballyhooly and Mitchelstown north earlier this summer.
The Environmental Protection Agency found no barrier had been fitted to prevent cryptosporidium from entering the water supply in Ballyhooly — a village between Fermoy and Mallow.
It has now called on Irish Water to prioritise the installation of a barrier to ensure the safety and security of the Ballyhooly supply.
The EPA said the supply was classified as being “very high risk” for contamination with the potentially dangerous parasite.
Cork County Council said it monitored land use and all planning applications around the source of the drinking supply — a spring located near the Awbeg River — due to its perceived vulnerability.
The council said it had reminded two local landowners within the buffer zone about their obligations under the EU Nitrates Directive.
Irish Water detected the presence of cryptosporidium in the village’s supply on August 9 but said no further examples were detected in a number of subsequent tests carried out on a weekly basis. On the same date, the bug was also detected in the supply serving the northern part of Mitchelstown and again on September 5.
No traces were found in three other samples taken from the supply in August and September.
The supply for Mitchelstown north is classified as at moderate risk for cryptosporidium but the risk assessment has not been updated in recent years.
The EPA expressed concern that sand filters for the supply had not been re-sanded in more than eight years.
It recommended Irish Water to review the cryptosporidium risk to the supply as well as to provide an update on catchment, farm and septic tank inspections in the area.
Cryptosporidium, which is a small parasite found in faecal matter, can cause fever, stomach upset, weight loss and diarrhoea.
While healthy adults will normally recover within three days, the bug can have more serious effects including potential death for elderly and very young patients as well as those with weakened immune systems.
The EPA warned in September that some 161,000 people are at risk of illness from possible exposure to cryptosporidium.
It claimed there are 25 public schemes, which supply drinking water to homes, schools, hospitals and businesses, that do not have adequate treatment to kill off the bug.