The pipe burst near the Crawley Avenue underpass earlier this morning (June 20), severing the supply.
A school spokesman said that, with no drinking water and no water for first aid or to flush the toilets, the decision to close was made at 8.25am.
All parents were contacted and asked to collect their children, while those still at the school were being cared for until their mums and dads arrived to pick them up.
When asked when the school would re-open, the spokesman said: "As far as we're concerned it's business as usual tomorrow."
He added that parents should bring their children to school tomorrow (June 21) unless contacted directly by the school via email or text message.
Nearby Ifield Community College remains open. A spokesman said: "We are fully operational and we have a full tank of water in reserve."
Southern Water has been approached for further details.
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