Greywater is the water that comes from sinks, showers and washing machines. Basically, everything but toilet water, which is called "black water".
Greywater systems are just in the process of being approved on a limited basis in Oregon.
In Oregon, you may only collect greywater into an approved factory built system. The "treated" greywater can then be used domestically for toilet flushing. This is quite limited but a step in the right direction.
We offer the only factory greywater treatment system that I am aware of, the Brac Systems
A report on greywater reuse for landscape irrigation by the Water Environment Research Foundation (WERF) in 2008 can be found HERE