It's interesting. One of them is "water use" and the other is "urban water use" but you're right - there's a lot of water use in the US comparatively speaking. Thing is, though, I spent a week in Amsterdam back intheday and I don't recall people using, like, half as much water. So I'm wondering if it's a processing thing?
I've attempted to research this more, but it is quite difficult to pin down why the difference is so huge. This report by the EPA breaks the US water use down to these components: And a similar image I found from my water company, but in liters (4L is ~1 gal): We use 50L for showering, you guys use 100L. We barely use any water for the garden - I think that's in the 1,8L or in the 5,3L slice - while you use 100L. I would assume most of that difference is in the efficiency of the showerheads and washing machines. I've noticed that the toilets here use much more water than back home.
So fully half the difference is the lawn. That figures. The US has steadily been switching over to low-water washers; that'll help, too. And Americans definitely shower more than anybody else. It isn't the showerheads, Americans straight up shower more often for longer. So... explain your toilets. Because I remember the toilets in Amsterdam being the worst design I'd ever seen in my life. That whole "poop on a shelf and hope the water washes it away after like five flushes" thing was really weird to me.
Well, most modern toilets don't use the shelf-thing. But I think it's mainly to prevent Neptune's Kiss. One thing that I noticed about the toilets here that you guys hold so much water in the toilet itself. It's almost a damn swimming pool.