They used a water gun?This is way over blown. Moving on.
I hope you were being sarcastic. A water based disruption device is an extreme high velocity blast tool that physically dismembers a device before it can detonate.
In many cases it can work, and this appears to be one.
But if it went off, aimed at you, it could rip an arm off your body, or cut you in half. It’s not a “water gun”.
http://www.youtube.com/watch?v=osHIh3Y_dQ8
In action, watch how it cuts through steel.