The coil side of a relay really doesn't care...
You can power either terminal and ground either terminal, and as long as the twain don't meet it will work...
you have 4 terminals...
coil 1
coil 2
input
output
The input is the high power for your load.
output is the load.
Coil needs ground on one side and power on the other to energize the relay.
A popular way to wire them is to connect INPUT and 1 coil TOGETHER and connect that to high power.
Then, to energize the relay, you just GROUND the other coil wire.
Sometimes, they spec one side of the coil is grounded. If so, you need to supply low current power to the other side of the coil. If in your main control panel, you can grab this from the tank sensors, or the water pump switch.