You sure about that?
https://agrilifeextension.tamu.edu/library/landscaping/xeriscape-landscape-water-conservation/Xeriscape has 7 steps:
1. Planning & design < don't buy all the plants without knowing where they're going to go
2. Soil analysis and preparation < you cannot put "too much" organic matter in the soil here.
3. Practical turf areas < see? You can still have a lawn!
4. Appropriate plant selection < doesn't have to be cactus. Also steer clear of azaleas.
5. Efficient irrigation < don't water the street, don't flood the landscape
6. Use of mulch < keeps the soil cool, adds organic matter
7. Appropriate maintenance < pruning here and there
Zeroscape is cactus and rocks. Or, if you're in AZ or NM, it's Xeriscape if you follow the principles above.
A typical backyard swimming pool holds around 15,000 gallons. Residential irrigation systems will use between 3,000 and 8,000 gallons per cycle (maybe less, maybe more).
Edit: I linked the same info already posted here. Oops.
The Extension Service and our Master Gardener group have great resources. For plants that don't need much maintenance once established, check out the list of EarthKind plants.