It's kind of a funny thing to say, because as the tagline itself mentions demand isn't (totally) fixed. It also doesn't give the source of that exact statement, annoyingly.
What's actually going to happen is that people some places are going to have scarcity and have to cut back or import more at a cost. Either gradually, the way it seems to be shaping up where I live, or suddenly, like whenever California's aquifers finally bite it.
Yeah I mean I wonder how much water would be saved in water scarce places if people just stop having lawns for no reason.
People can put actual effort into their homes exterior and invest in native grasses and plants that way. Save a lot of water and end our troubles with toxic runoff