Water is one of those resources which flow and circulate. They don't get "used up" so much. It is used in its many forms, liquid, gas and solid and its transitions from one state to the other is often useful. It is temporarily held within bodies of produce and other products and in people as well. But these are molecules which circulate all over. The water molecules which are in your body right now may have previously been in a T.Rex long ago at some point.
Now, some states and conditions and situations of water aren't "usable" at the moment and it would take some time before it gets to that state. Which leads to the main issue of water conservation. That main issue is how much is available at any one time in the appropriate state and condition at the right time and in the right place. Under circumstances when resources are presently insufficient, the next question is cost and time to achieve the desired resource levels.
I guess what I'm getting at is the understanding of not "how much is used" but "the rate of how much is available minus the rate of how much is used." When you get negative numbers, it's a problem... obviously. But for people to just say "how much is used" denies people a bigger understanding.