What boat do you have?

There will be a Thru-Hull Intake, one or multiples ones depending on your boat, I would turn off the Bronze Ball Valve (emergency shut off valve). That would prevent any water from entering the ballast system.

As for your switches, depending on your boat model, you can also kill the power to your switches via fuses. That will prevent someone from bumping the switches, not running water thru the pumps, that would wear-down your pumps. As Scott mentioned, on older sprinkler systems the manifold will have an electronic solenoid sprinkler valve (Orbit Brand).