I must admit I am puzzled. It seems to me your recent most informative post was the answer a question that wasn’t asked.
Arguably the Earth represents a closed system. I don’t imagine much water is being lost to space (though admittedly I haven’t researched this). Thus water is simply moved from one place to another over time. None is actually “lost”. The problem we are facing with draught, then, represents a change in the location or form of the water, not an actual decrease in the amount of water in the system (the entire planet).
Of course, this doesn’t actually help anyone who is currently feeling the effects of water shortages since relocating water is not an easy task. As you imply in your answer, the fact that ocean levels are rising doesn’t help since converting salt to fresh water is not seen as economically viable.
I certainly don’t have to tell you that the location of water has been a contentious issue for much of recorded history. Wars big and small have been fought over this. I’m just not sure how shorter showers is going to mean more water for a farmer 1,000 miles away.
We may not lose water, but we do lose Hydrogen (one of the first studies I read was about the changing composition of the atmosphere from the Palaeoproterozoic or whatever - didn’t really understand it).
The question that was asked was whether water conservation (“not wasting water”) was a good/useful thing. Cecil’s answer was focused on the LOCAL question rather than the global question. From a local perspective, yes, not wasting water is good. From a global perspective, it perhaps doesn’t matter.
Sort of like asking, “Is it good to have airbags in the car?” The LOCAL answer is yes, it’s protection. A global (long-term, big perspective) answer would be: you’re going to be dead in 100 years anyway, so what’s the difference? I think most readers would agree that the long-term, big perspective answer is unsatisfactory.
It’s simple-ish. The atmosphere, is held around the earth by gravity. Sunlight makes gas molecules warm (or even hot), they fly very high into the atmosphere - gravity eventually slows them down, and they fall back to earth cooler.
Occasionally, the gas molecules go so fast they escape the earth’s gravity and we lose them to outer space. But it’s not much, so we don’t really notice.
The biggest problem with “wasting” water is that it takes energy to filter and distribute water, so “wasting” water is really more like wasting energy. Of course, there are areas where water supply is a concern, so “wasting” water in this case also means straining the available supply (thus why you get lawn watering bans and the like during droughts).
Also, desalination of salt water into fresh water is economically viable, and rapidly growing as a source of fresh water, although at a high energy cost (getting back to the first point I made above), mainly in Middle Eastern countries (half of Saudi Arabia’s water comes from desalination) but also islands and areas with persistent drought:
