Would you like to post a link to the legislation that allows them to do
this?

Only if you post a link to the legislation that says they cant.

Water Industry Act 1991 (c.56)

http://www.opsi.gov.uk/acts/acts1991...10056_en_8.htm

37-38 Places a duty on the water company to supply water.

http://www.opsi.gov.uk/acts/acts1991...n_8.htm#mdiv52

52 Places a duty on the water company to supply enough water for domestic
use.

http://www.opsi.gov.uk/acts/acts1991...10056_en_9.htm

76(1) Enables them to break this duty for the purposes of a hosepipe ban,
but only for car washing and watering gardens.

Your turn.

Christian.