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.