Jetta heater water tank leaks, can it not be replaced? Will it affect driving safety?

It won't affect, as long as the warm water valve doesn't leak, it's no problem! When the warm air is not turned on at ordinary times, check whether there is water leakage. It doesn't matter if there is no water leakage. The air conditioner can't keep warm! Yours should be a manual air conditioner, there will be no problem and there will be no impact on safety. Usually pay more attention to whether the coolant is lacking! I hope it works for you.