Some people living and working in parts of Norwich and Thorpe St Andrew may have no water after an issue affected supply.
Anglian Water said it had been made aware of the problem at around 10.30am and is investigating the cause.
The utility firm said the issue is affecting parts of central and east Norwich, including areas of Thorpe Hamlet and Thorpe St Andrew.
Some homes and businesses in those areas may have very low water pressure or no water at all.
Anglian Water is urging anyone who has spotted a leak in the area to get in touch after its systems indicated it may be the source of the problem.
It added it will provide updates once it hears from a team of engineers sent to investigate the cause.
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