How do you enable a button to make water deadly?

I’m going back to an old Trouble in Terrorist Town map that I made and want to add some more Traitor traps. I already understand buttons and traitor buttons, but I’m not sure how to do what I’m trying to accomplish.
I want the water to be activate-able in a way that when activated, it will become deadly to anyone that touches it.
I’ve seen this done before but can’t figure out how to do it myself. All help is appreciated.

Just make him as big as the water brush, use the trigger texture. Then you can use your button to enable/disable him

I’ve got to go at the moment, but I will look into this. Thanks!