Electronic Alarms and Home Security Devices - DSC832 - Adding water sensor(s)

I would like to add a water sensor for the tray beneath my water heater to a single zone on my DSC 832. My LED keypad has 8 zones, 2 are currently free. The second zone will be used for my monitoring my garage (separate pos).

Running a wire is not a problem. I just some product suggestions (links) and any other words of wisdom.

Expanding my thinking a bit ... if the sensors are not too expensive and three can be combined into the same zone circuit, I would like to also include sensors for my A/C drain overflow plans.

Suggestions and recommendations welcome.

Thanks

Most of these things are just passive devices, so you can put multiple on the same alarm loop. They wire into the system like a motion detector (4 wires-2 for power, and 2 for alarm loop)

Here's a fairly standard example: http://www.grisk.com/specialty/2600water_sensor.htm