Two schools were forced to close after a burst water main in Huddersfield.
Hundreds of homes and businesses in the Birkby and Hillhouse areas were also hit by the burst on Tuesday morning.
The main burst at the junction of Blacker Road and Edgerton Road.
Contractors tried to ease problems by turning a valve but that many more customers lost supplies.
The two schools that were hit were Birkby Juniors and Birkby Infants and Nursery.
Mrs Susan Davis, head at the Junior School in Mead Street, said: “We understand that a burst water main had affected quite a wide local area, including our school.
“Having no water supply meant we had no toilet facilities for 70 staff and almost 500 children, so it was not possible for us to remain open.
“The decision to close for the afternoon had to be taken and we informed parents immediately.”
The Infants School also had to close with children sent home if parents or guardians were available.
But many returned home to find their homes were also left without water.
Yorkshire Water said more customers in Birkby and Fartown lost water supplies than anticipated when employees turned a valve on the system to try and isolate the burst.
When the error was realised, the valve was returned to its original position.
The problems for the workmen were exacerbated because the burst is in the middle of a busy crossroads and a four-way traffic light system had to be set up.
A Yorkshire Water spokesperson said: “We apologise to anyone in the HD1 and HD2 areas of Huddersfield who are affected by our burst water main.
“Our employees and contractors are currently on site, at the junction of Blacker Road and Edgerton Road, and we expect to have repaired the water main by the end of today.”