This isn't the fire engine I originally intended to show, but work on that one hasn't progressed as fast as I had hoped. So here goes with a water carrier (WCr).
A modern UK fire engine carries 1800 litres of water and a pump with a maximum throughput of 2,200 litres per minute. Normally, fire engines use the water in their tank initially at a fire and as soon as possible connect their pump to the mains water supply via a hydrant. However, in rural areas there can be problems with mains water supplies because of low mains pressure. (When I was a volunteer photographer with my local brigade, the criteria for calling me out to a fire was if it required four pumps or more. Almost invariably, however, the problem was one of poor water supplies with one fire engine fighting the fire and the other three keeping it suplied with water, rather than a "goer" - i.e. a good big fire.) As a reuslt, brigades covering rural areas often have a WCr with a 10,000 litre capacity tank. This can ferry water to the scene of a fire, dump it in one go into a portable tank which the appliances fighting the fire can then use, while the WCr goes off for more water.
Copt Hewick Volunteer Fire Brigade covers a largely rural area and, like a real fire brigade in similar circumstances, has a WCr. This was built in the brigade workshops using the chassi from a 3880 fire engine and the tank from the airport refueller. The 3880 chassis needed a bit of building work on it to support the tank.
Here are the first three pics.