How do I get a permit for a graywater system?

For watering the landscape: In Oregon, the DEQ’s Graywater site provides a comprehensive guide to permitting graywater systems. The DEQ’s Graywater Homeowners Guide provides the same information in a more readable format.
For other areas, Greywater Action’s Codes and Policy page provides an overview of the state of graywater codes on a larger scale. Contact your local environmental health authority for more specific information. 

For reuse for flushing toilets: Oregon created a permit pathway for commercial and residential wastewater conservation systems that flush toilets and urinals in 2008. To date less than a half dozen projects in Oregon have utilized this option.

Oregon Building Codes Division’s Smart Guide to Water Conservation Systems describes how to design, plan and permit a water conservation systems that reuses wash water for toilet flushing.