tiff,

My logical answer to your question is yes. But you live in California and they have rules on "Grey Water". The City permit office would know the rules and if you ask them then they get to tax and fee you(your a commercial venture). That being said you need to determine how often you back-flush(total gallons per time period). Determine your flow rate(gallons per minute) when back-flushing. If you can move the back-flush under pressure you can store it in a tank or holding pond to dissipate the chlorine and use at your convenience. There should many irrigation experts in Napa Valley. The vineyards probably have them on speed dial. They can design you a custom system. You could even sell water to others. Get more than one company to give you a design and we can help you evaluate the proposals. Good Luck aloha