Lower Dauphin School District officials discovered the water supply at Conewago Elementary was contaminated with coliform and E. coli during a routine check Tuesday.
The school uses well water and was placed on a water boil advisory.
The district sent a letter to parents informing them they are working with the state Department of Environmental Protection to take the necessary steps to get rid of the contamination.
Officials will flush chlorine in the water system to kill the bacteria.
Until then, students and staff are drinking bottled water and using hand sanitizer.
The goal is to have the water system safe by Monday.
Two clean samples must be taken on two consecutive days before the school can resume using the well water.