Southern Water was made aware of the burst water main shortly after 4am this morning.
A team was sent to the site in the PO30 5JH area of Hunnyhill to isolate the broken pipe and make the necessary repairs.
At 10.20am, the water company confirmed that most of those affected should have running water, however, some residents in the Riverway, Dodnor and Sylvan Drive areas are still without supply.
Alternative supplies of water will be delivered to the area, says Southern Water.
A spokesperson said: “Due to the complexity of the repairs, the burst will take some more time to fix.”
“We’re working hard to make repairs and get things back to normal.
“Again, please accept our apologies for any inconvenience caused.”