His water bill must be...

I think the link you gave points to Patrick Blanc's house in Paris not one of his projects in Sydney. Water use might not be as high as you think. I cannot find details of this design but many of his projects are watered by systems that use locally collected water. Also he makes a point of choosing plants that suit the site which is always a plus, compared to those who want to grow lawns in the desert.

Also explains why I confused arid Australia with "normal rainfall" Paris.

Still, maintenance alone must be time-consuming, unless he has a part-time gardener to prune and clean.

Just servicing my city garden is time-consuming!!! Plus, of course, in my climate ya gotta water. Our City makes strenuous efforts to get people to convert to xeriscapic landscaping; there is even a subsidy. One of these y ears I'll get around to it, unless I run out of time...

HB