This can create thermal shock which causes the glass to expand and crack under the pressure.
However, motoring experts have urged caution over the simple trick, claiming there was still a big risk of vehicle damage.
Neil Greig, IAM Road Safety expert warned the melted water could “refreeze” in windscreens and even risk “icing up locks”.
He said: “Anything involving applying warm water to a frozen windscreen does risk causing a crack or making an existing one even worse.
READ MORE The melted water may refreeze on wipers or in the engine compartment and using it on a side window also risks icing up locks or door handles.