You might be eligible for a reduction in your sewer rates — contact the San Francisco Public Utilities Commission, High Consumption Unit at (415) 551-4780. You’ll be asking for a reduction in the “flow factor” for the sewer. They’ll send you a form to fill out and have an inspector visit your home. If you aren’t happy with the outcome, you can file an appeal and make your argument for a reduction in rates in person before the community board. I did this once and was successful in getting our flow factor rate reduced. It helped to have a table listing the water usage over the years — which showed heavier water usage during the months with no rain. Photos of the garden also helped.
Information on “Flow Factor Appeals” (reducing the sewer rate), from the SF PUC website:
“Residential users may be eligible for a reduced flow factor if they are using large amounts of water to irrigate a lawn or garden and believe their annualized irrigation consumption is greater than 10%. Customers may request that their flow factor be reviewed by filing an appeal for a reduction of their sewer service charge.”
The SF PUC web site, for other information, water conservation ideas, the PUC gardening calendar, etc: