A burst water main is affecting all BN17 postcodes, forcing the civic centre to close.
This afternoon, Southern Water tweeted: "We’re currently working on a burst main affecting the BN17 area in #Littlehampton. Our crews are on site working to repair and we expect the water to be back on within the next couple of hours.
"We're sorry for any inconvenience caused and would like to thank everyone affected for their patience while we work on this emergency."
In an updated statement sent at 4pm, a Southern Water spokesman said: "We're sorry to say a 10 inch water main in Littlehampton has been damaged and homes in the area may be suffering from low pressure or no water.
Our teams are already on site and preparing to fix the burst. In the meantime we have re-zoned water supplies in Littlehampton and things should be returning to normal. We'd like to thank everyone for their patience and understanding and we apologise for the disruption this incident has caused."
Due to Littlehampton's flat and low lying geography, it may take a while for supplies to return completely to normal, the spokesman added.
A spokesman for Arun District Council said: "Due to a burst water main affecting all of BN17 postcodes including the Civic Centre in Littlehampton, we have had to close the Civic Centre from 3.00pm today.
"Members of the public will still be able to use our on-line facilities and the appropriate messages will be loaded on to our telephony system. We are advising customers to keep an eye on our website banners and social media channels for updates.
"Bognor Regis Town Hall will continue to operate as normal."