No need to drown em out and besides the water would most likely saturate into the earth before it reached the rabbits.
Sit and wait em out. Buy yourself a Camo Net a few short poles and lye under the net about 30 yards away from the warren and wait for em to come out. Another way is BLOCK one of the holes and sit and wait at the other.
I DO have plans for a WMD of the rabbit type but current legislation prevents me from disclosing the specifics to you due to the fact when it goes off it will wipe out a whole 20 yard area of life
Zeb