Students at a Victorian high school have unknowingly been drinking water recycled from a sewerage treatment plant for more than a year.
South East Water says a recycled water supply line was connected to a drinking fountain at St Peter's College in Cranbourne.
The health department understands the line was connected in December 2013 but how and exactly when that happened is being investigated.
The issue was detected by a maintenance worker on April 1, who immediately notified South East Water and had the supply cut-off.
Health department assessments indicate the risk of illness is low but it may have led to a slightly increased risk of gastroenteritis.
St Peter's Principal Tim Hogan said the school and health department will hold a meeting for concerned parents and students tomorrow.
"The calls I have received from parents are about students feeling a little bit anxious," Mr Hogan told AAP.
The school has not recorded any spike in illness, and records do not show any evidence of a gastro outbreak.
An assessment of chemicals possibly present in the water found the vast majority were at very low concentrations and unlikely to be harmful, although further assessments are being undertaken on a small number of chemicals.
The water is the highest class of recycled water and is intended for residential gardens and the irrigation of crops.
