Water is a pretty powerful thing. It can bend metal, cut even the hardest materials or crush anything. Japanese yutuber under the nickname Asp used the power of water to create a powerful water cannon, and it looks very intimidating.
The author does not give information on the design of the gun, but it can be concluded that the water is stored in the reservoir, where it is fired by compressed air under high pressure. Such a scheme gives the water enough acceleration and power to break glass, CDs and who knows what else it is capable of.
One thing is for sure. In any game in the “war” on water pistols to the owner of such a thing, the win is guaranteed.