Pittsburgh - A water treatment problem in Pittsburgh has led to the closure of nearly two dozen schools and a boil-water order for 100 000 customers.
The Pittsburgh Water and Sewer Authority says the water doesn't have enough chlorine. Officials say that could enable giardia, a parasite that causes severe diarrhoea to grow.
The low chlorine level was discovered by US state environmental officials. They have been testing the city's water as part of an ongoing investigation into its water treatment system.
The problem prompted Pittsburgh Public Schools to close 22 schools and two early childhood centres on Wednesday.
The advisory was expected to last up to three days. The city is setting up distribution points where residents can get bottled water.