There is a leak in the small heater tank. Can I still drive?

First of all, the liquid leaked from the water tank of the small heater you mentioned is actually the engine coolant. If the water tank of the small heater leaks, the coolant level will decrease, which may cause the cooling system to work badly and the engine to overheat. Therefore, it is not recommended that you continue driving when the water tank of the small heater leaks.