I haven't studied the documentation on the G. Risk water sensor but what I
think they are saying is you need a minimum of five volts from the zone, using an EOL resistor, without the zone violated.
From what I'm guessing, the Elk's zones, when used with an EOL resistor will have a "range" of voltage, I think somewhere between seven to ten volts (can't remember exact numbers as it's been a while since I messed with an Elk). This is of course for a normally closed sensor. If the voltage goes up over ten (i.e. zone is now "opened" or tripped) the zone will show violated. If a wire shorts for some reason, the voltage will show less (and some trouble/violation message will appear).
If the Elk used a smaller voltage for an EOL unviolated zone (say under five volts) you couldn't use this sensor. Of course there is also the issue of making sure that zone had enough current capability to drive that sensor.

I would also have to scratch my head when trying to parallel these sensors to one zone.
Let's see what other say...
EDIT: Also note that G Risk makes water sensors with a built in contact relay that would wire much like a glass break or motion sensor:
http://www.grisk.com/specialty/pdf/2600.pdf
http://www.safemart.com/index.asp?PageActi...amp;ProdID=6277