While I poked at ice at home, in metro Chicago they were battling a warehouse fire..and ice. There must be a way to heat the water coming out of the hoses--I mean you already have the built-in generator of the truck, and the firefighters apparently use road flares around the hydrants to keep the water from freezing at the connection. Here are more photos:
Top photo is from the AP, others are Chicago Tribune. Below photo credit: Jose Osorio, Chicago Tribune.