In July I took a shower at a marina in Annapolis Maryland. The shower didn’t have a flow restrictor and it was marvelous. In California the luxury of a full flow shower has been legislated out of existence. It sounds like an opportunity to me.Why not build a shower with a holding tank that recycles some of the water so that you can have more flow with no increase in actual water usage. A quick search shows that there are some companies playing around in this space already but nobody appears to have much traction yet.
The trick would be to make one that works that is expensive and markets to the very rich enviro-conscious. The same people who pay someone to create an organic garden for them. This is a work around a Nanny State restriction an could make some enterprising inventor rich.