What is "throw cold water on"

Usage examples of "throw cold water on".

I thought about having Dean throw cold water on her, but that would just steam the place up and cause the wallpaper to peel.

Matthew felt sure she would throw cold water on his project at once.

Certainly I can't see why anyone connected with Uncle Sam would want to throw cold water on a plan to fortify the canal, even if an outsider has invented the gun--I mean someone like myself, not connected with the army or navy.

I'm Mayor-Ira does the work, but I bang the gavel at community meetings-there are always colonists who think that a colony can operate like a big-city planet, so I preside to throw cold water on damfoolishness.

I have not seen the work of Sonnoni which you mention, but I have seen another work on Africa, (Parke's,) which I fear will throw cold water on the hopes of the friends of freedom.