If the hose reel is connected to a dedicated fire-fighting supply, then this might be an offence under the Water Industry Act 1991:
"73.—(1) If any person who is the owner or occupier of any premises to which a supply of water is provided by a water undertaker intentionally or negligently causes or suffers any water fitting for which he is responsible to be or remain so out of order, so in need of repair or so constructed or adapted, or to be so used—
(a) that water in a water main or other pipe of a water undertaker, or in a pipe connected with such a water main or pipe, is or is likely to be contaminated by the return of any substance from those premises to that main or pipe;
(b) that water that has been supplied by the undertaker to those premises is or is likely to be contaminated before it is used; or
(c) that water so supplied is or is likely to be wasted or, having regard to the purposes for which it is supplied, misused or unduly consumed,
that person shall be guilty of an offence and liable, on summary conviction, to a fine not exceeding level 3 on the standard scale.
(2) Any person who uses any water supplied to any premises by a water undertaker for a purpose other than one for which it is supplied to those premises shall, unless the other purpose is the extinguishment of a fire, be guilty of an offence and liable, on summary conviction, to a fine not exceeding level 3 on the standard scale."
... could be an offence under both (1) and (2)?