Here is the homework behind the advice.

We link to public Extension and agency sources, label estimates as estimates, and try not to pretend one watering schedule fits every yard. Below is what we used and how to check it yourself.

Rainwater calculator

The calculator uses about 0.623 gallons per square foot for each inch of rain, then applies the collection-efficiency percentage you choose. It is a ballpark. Roofs, gutters, first flush, and storage all have a say in what makes it to the tank.

Core references

• University of Arizona Cooperative Extension: RainScapes
• University of Arizona Cooperative Extension: watering newly planted desert-adapted plants
• University of Arizona Cooperative Extension: recommended plants and watering needs
• Arizona Municipal Water Users Association: Plants for the Arizona Desert
• Arizona Department of Environmental Quality: Using Gray Water at Home
• Arizona Administrative Code, Title 18, Chapter 9

Scope and updates

This first edition focuses on Arizona's low desert. Regional guidance may not apply at higher elevations or outside Arizona. Any future geographic expansion should use local Cooperative Extension and agency sources.

Pages that discuss rules include their source and a check date. We aim to review official policy references at least quarterly and after we learn of a rule change. If a source changes, the official agency publication controls.

Last source review: November 4, 2026. Independent educational project. Not affiliated with the linked organizations.