Tap water in parts of Whanganui is running discoloured after dirty water entered the city's reticulation system following emergency repairs on Wednesday morning.
Most of the homes affected are in the Castlecliff area but there has been discoloured water throughout the city since Wednesday afternoon.
A council statement said the water was safe and was still be chlorinated.
Residents are advised not to run their taps as "it's better to conserve water until the problem is resolved".
"Veolia contractors are working on flushing the mains in the affected area and will continue until the system is clean," the council said in a written statement.
"After investigation it appears this has come from an emergency repair completed early yesterday morning.
"Unfortunately dirty water has entered into the reservoir and then gone out into the reticulation affecting Castlecliff."