Cambridge Water supplies drinking water to about 350,000 customers across Cambridgeshire and parts of Hertfordshire, including Cambridge, Ramsey, Gamlingay, Balsham, Melbourn, Royston and Baldock.
Its ban, announced on Thursday, is also with immediate effect, with restrictions becoming enforceable from 01:00 BST on 17 July, a spokesperson said.
Managing director Elena Karpathakis said: “This is not a decision we have taken lightly – it is the first time in more than 30 years, since the UK drought of 1995, that we have had to introduce a temporary hosepipe ban.”
Speaking on BBC Radio Cambridgeshire, the company’s director of water quality and environment, Natalie Ackroyd, said it was committed to removing the ban “as soon as possible”.
“That will depend upon demand reducing to more normal levels and our water resources being in a more healthy position,” she added.