have you seen the demo where Erickson drops a water salvo (2000 gal) on a car with the Skycrane?
(I'm trying to find it)
flattens the car and pushes it 200 yards down the road!
Let's see... Water weighs about 8 lbs a gallon. Multiply that by 2,000...
16,000 lbs of water. Of course, you could just take the 2,000 gallons and transfer it directly to the weight of water, coming up with 8 tons of water. 2,000 lbs is a ton, after all.