Some basic napkin math says at normal temp and humidity that is roughly 84 cubic miles of air you'd need to reduce to 0% humidity. Assuming the process isn't instant, you couldn't contain that volume of air in a structure humans know how to build. You'd also have to build massive air inlet pipes going 5 miles in each direction just to be able to circulate it into the machinery.
Edit: the comment I replied to was talking about areas with "humidity but not rain." I was just pointing out trying to replace rain is an insurmountable problem. You can do all sorts of things to optimize water usage, but that isn't the point. I picked San Francisco because it is a scale most people on HN can understand, but it is still tiny compared to farmland in the central valley.