Well, if the stuff re-freezes, you're not exactly better off, are you?
CRJ700 (and I think our other products) advice use of hot water (nozzle temp 60 degC or greater) for
deicing only for temperatures of -3degC or greater. So if you're talking of temps down to -10degC we would NOT recommend use of water alone as a deicing agent.
We also do not recommend use of hot water as part of a 'one step' process - it's only recommended as the de-icing step of the two-part process, where the second step is application of anti-ice fluid. The guidance suggests that the second step be applied before the first stage refreezes, and warns that this may be as short a time as 3 minutes.
Based on that, I'd say that hot water alone is probably worse than leaving the frost there - though that doesn't make either of those a good idea.
usual caveats about your OEM's advice, and local regs, of course.