I don't doubt that in arid and semi-arid areas, humans are doing things such as using up groundwater faster than it can be replenished. But surely what the people of Utah are doing with their groundwater is irrelevant to the conservation decisions of the citizen of North Carolina. There are no plans that I know of to replenish Utah groundwater with rain falling in North Carolina. For those of us who live on the rainy East Coast, the only question I would think matters is, "Are we using up our local fresh water faster than it is being replaced?" And clearly we are not, given the huge amounts of it I see flowing by unused whenever it rains.
And of course, the argument for taking short hot showers is untouched by the above considerations: We might want to take brief showers on the East Coast in order to lower our carbon footprint.
Why worry about this at all? Well, attention is not costless. When we direct people's attention towards fixing non-problems, they have less attention to direct fixing real ones.