How do people justify that? Let's assume daily showering these days is shaveh le-chol nefesh, still, that should only permit heating water on YT but not taking water from the tap and heating fresh water that you're not even using, and secondly, isn't there still an issur derabbanan to shower in a shower lest you come to bathe your entire body?
why would you be using water unnecessarily? secondly, the is no problem to bathe your whole body, just a problem of changing substances eg. soap.