There is a GUI condition to detect water, its a Boolean thing. I'll open up the editor and get the line
______________________________________________________________
Water Check
Events
Time - Every 0.50 seconds of game time
Conditions
Actions
Set TempPoint = (Position of (w/e unit))
If (All Conditions are True) then do (Then Actions) else do (Else Actions)
If - Conditions
(Terrain pathing at TempPoint of type Floatability is off) Equal to True
Then - Actions
Set TheGuyIsInWater = False
Else - Actions
Set TheGuyIsInWater = True
Custom script: call RemoveLocation(udg_TempPoint)
______________________________________________________________
Ummm something like that XD
Then you can use the Boolean variable elsewhere in another trigger.