At least 80 elementary school children in Queens, N.Y., were hospitalized Tuesday after drinking from a contaminated water fountain.

Two city buses were required to transport students from Public School 20, John Boone Elementary School, to local hospitals. The students began complaining of stomachaches and nausea after consuming water from a fountain located in a new wing at the school. According to officials, all students have been treated and released.

A contractor working on a broken air conditioner system may have leaked a type of anti-freeze into the drinking water supply, said Margie Feinberg, a spokeswoman for the Department of Education, to The New York Times.

The air-conditioning chemical, propylene glycol, also caused the water in school’s toilets and fountains to turn pink.

Anti-freeze is a sweet-tasting substance, which may explain why the children continued to drink the tainted water, said Dr. Glen Asaeda of the New York City Fire Department to the New York Daily News.

Investigators with the Department of Environmental Protection, the Department of Health and the Department of Education claim the air conditioning contractor, Bayside Refrigeration, is to blame for the incident.

The school’s water supply has been shut off, and bottled water is being provided to students during the investigation, Feinberg said to The New York Times.