As far I'm aware, there is no way to disable it. According to the vehicle market, Tankers are required once you have constructed your 7th fire station.
Water tank equipment does exist, however, I've not personally tested it.
There is also the pumper tanker, a multi purpose vehicle that serves as both a Engine and Tanker simultaneously, however, if you've yet to reach the rank of Captain it will cost coins.
Overall it seems that the Utility does not serve much purposes besides towing water based units or transporting extra crew members. , yet is required to be purchased upon your fourth fire station. Neither can it respond to a call that only needs it due to a fire engine being required on all fire and rescue calls. I think it could be used to perform as something such as a light rescue and to allow for some missions to only require at most a utility or a Utility and Engine in order to give it more of a purpose rather then filling garage space. Some calls require a Heavy Rescue when maybe a Light Rescue could be an alternative to having to use a heavy rescue on most rescue call outs.
