Greywater systems are not widely used here in Phoenix, but could provide a fantastic opportunity for water re-use and conservation here in the dry Phoenix desert. Greywater systems re-use water from your shower, laundry, sinks and dishes (pretty much everything except the toilet), rather than sending it down the sewer system. The most common use of greywater is for landscape irrigation, which saves the cost of watering your lawn with freshwater. It's estimated that 50-80% of your household wastewater is greywater.
In using greywater for landscape irrigation, ADEQ (Arizona Department of Environmental Quality) regulations require that the greywater be filtered and disinfected before being sent to a sub-surface irrigation system. It's not a good idea to take your washing machine hose and just drain it on your lawn or in your bushes. Surface greywater can tend to pool up, and if it hasn't been filtered, may contain bacteria that you don't necessarily want sitting on top of your lawn and plants.
On the other hand, greywater can be more beneficial to your plants than freshwater because it may contain nitrogen or phosphorus, which will help your plants grow stronger and healthier than with freshwater alone.
Greywater systems can be expensive to have installed, but it's worth doing some research into them if you're looking for more ways to make your home environmentally friendly.