There are two important things to remember:
1. You must know the input voltage of your water pump.
Most of them are 12V AC and 12V DC.
The 12V AC and 12V DC power supplies are different, you must choose the right one according to your water pump specification.
2. check the power consumption of your pump, this is also important.
ATTENTION: For water pumps, use the transformer at max. 60% load.
As the water pump needs a high current in a short time when starting up, this current exceeds the nominal power consumption of the water pump, so that the power supply can be damaged very easily.