Students and staff at Harrogate Grammar have been sent home after the school has suffered a leak to its main water supply.
Lessons, year 7 parents evening, Remembrance evening and all other school activities for today have been cancelled.
After the problem developed earlier this morning, parents and carers were sent an urgent message saying that their children would be sent home between 10 and 11am.
In his email, head teacher Richard Sheriff said: "I have no option but to close the school site for both students and staff.
"The extent of the leak and its impact on our school only became apparent once students had started to arrive with us this morning so we are now faced with having to send them home during the school day.
"I am extremely sorry for any disruption or problems this may cause you, but the circumstances are completely beyond our control."
Whilst the school has more than one water supply point, Mr Sheriff explained the problem is affecting most of the toilets ans water points throughout the school.
He said: "Whilst we do have water for our kitchen, we are not able to provide the basic facilities to keep children and staff healthy and safe."
Students who require buses to get home or have no safe place to go to during the day are being accommodated for in the school's Sixth Form area.
Catering and limited access to the toilets is being provided in that area of the building.
Yorkshire Water have not yet been able to attend the site and so the school has no indication of when a repair can be made.