There are many reasons that can make your small hot water heater Leak.
First of all, you do not have to fill up the hot water heater more than its capacity because it is smaller in size.
If it is undergoing any kind of corrosive effects this can also be one of the reasons your hot water heater is leaking.
You need to get your hands on one of the best hot water heaters so that you do not go through this problem.