Thanks for all the thoughts!
It is interesting that so many of you are suggesting trucking in water; I'll have to look into that. I could probably combine some water catchment with a big tank that could be topped up with trucked water IF it is not prohibitively expensive.
I could, in theory, dig a pond, but I'd still need water to fill it; I'd get into trouble if I use any flowing or ground water, though it could be used as cheap water storage. (Until recently, catching rainwater was illegal! It is still a grey area in the law.)
Catchment is a bit limited in that I'd need an equal area of catchment and growing area.
This last year I gardened about a thousand square feet on a three quarter acre lot. In addition to my garden, the owners had some lawn and gardens, though there was a lot of unirrigated space, and they were not crazy about the lawn. The water bill for the irrigation months was well over a thousand dollars; their winter bill was about thirty dollars a month.
I'm tossing around a few catchment type ideas here. https://permies.com/t/94064/Alternate-rows-plastic-sheeting-dryland#770254