Graywater is tap water that has already been used for one purpose (commonly washing clothes or people) and then instead of going down the drain is diverted to landscaping to water plants.

Things to know about graywater for health and safety:

When the graywater gets out to the landscape, make sure the exit point is buried in mulch because graywater should not be sprayed in the air or come in contact with edible parts of plants.
Graywater should not be used to irrigate root vegetables.
Graywater should not be stored--you need to use it within 24 hours and no puddles. You'll be watering live plants, so choose non-toxic detergents and soaps and avoid salts, boron, and bleach.

No building permit is required when planning to divert water from a clothes washer, but other diversions might. Contact the Building Safety Division at (408) 730-7444 or email Building@Sunnyvale.ca.gov for more information.