alcohol... that's what most of the de-icer sprays are, anyway, just dilute industrial alcohol.
Cold water may move some ice for a while but it's likely to refreeze
Lukewarm water, maybe... hot/boiling water, never.
The best option is to start your car, get the heaters going and then go back inside and have another cup of coffee... :-)
Or invest in an electric block heater, and a timer... so that the engine/coolant is already hot when you start up, and your de-icers work quickly
I once had a Saab which even had a timer to switch on the electric seat-warmers, ready for you... now there's a company who understand cold weather :-)
"Two meters of snow, an SUV full of computers to deliver from Oslo to Kongsberg, and we're wearing dark glasses.... Hit it! "
(Probably one of of the most exciting rides of my younger years...)