Connecting Three 12V DC Water pumps to the same power source
Assuming the power supply can handle all 3 pumps turning on at once, this is what your circuit should look like:







simulate this circuit &ndash; Schematic created using CircuitLab

(Please ignore the "bulb" element, CircuitLab doesn't have a good motor/pump element)

Make sure that you pick a switch that can handle the load through the contacts.

If the pumps all pull from the same liquid and empty into the same container, they should pump 3 times as much in this configuration. They don't have to be plumbed in series for this to happen.