Authorities have been forced to close a canal, linking dams in Sydney's south west to the Prospect Waters filtration plant, because of Cryptosporidium.
The Sydney Catchment Authority says the closure is a precaution because levels of the parasite were detected in a channel, which supplies one fifth of the city's drinking water.
However Catchment spokesperson Alison White says households are not at risk.
“The Cryptosporidium that was found in the upper canal was in the raw, untreated water and it is very important to emphasise the fact that there was no Cryptosporidium found in the treated drinking water at all.”
“The tap water is absolutely perfectly safe to drink.”