I think it’s unfair to downvote you for playing devils advocate here, especially when you’re making it obvious that that’s what you’re doing. People should do better and rather challenge themselves to explain why you’re wrong in a way that can convince the devils advocate. It serves as a nice exercise for re-thinking your position and arguments.

For my attempt: They’re “wasting” water in the sense that liquid water at ambient conditions is a limited resource. They’re taking that water, and either turning it into steam, or heating it a lot before releasing it back to the environment. Both uses reduce the amount of liquid water at ambient conditions available in reservoirs connected to infrastructure made to extract it for public use. That is the resource we use for everything from drinking water, to showering and cleaning, to making food and filling radiators.

You could say that “wasting water” is imprecise, but I would argue that it serves as a convenient shorthand for “wasting liquid water at ambient conditions accumulated in reservoirs that are connected to extraction and treatment infrastructure”, which becomes a mouthful when you say it often.