The Sonoma Valley County Sanitation District (District) completed a study aimed at giving residential customers a way to exercise control over part of their sewer bills while encouraging water conservation. This page describes the fixed billing calculation method and volume-based method that replaced it. It also gives ideas on what you can do to reduce your costs with the volume-based rate. Note that the volume-based rate structure only applies to residential accounts with connections to both water and sewer, not commercial accounts and not those residential accounts without a water account through Valley of the Moon Water District or City of Sonoma.  For example a condominium unit will often not have an individual water meter account and thus would not be included in the volume-based rate structure.  The excluded residential accounts will stay on the fixed rate billing structure.

The Fixed Rate Billing Calculation

The Fixed Rate Billing Calculation still applies to these types of sewer accounts:

• Commercial Accounts
• Residential accounts with a sewer connection but without a water account through Valley of the Moon Water Distrct or City of Sonoma (i.e. on their own well)
• Residential accounts without an individual water meter (i.e. apartments, condominiums, and mobile homes)
• Residential accounts with a Public Water Connection but no water usage in winter months

Fixed Rate sewer bills are calculated based on usage of an Equivalent Standard Dwelling (“ESD”). An ESD is defined as what an average single family home would use in a given year.

The Volume-Based Rate Billing Calculation

The Volume-Based Rate Billing Calculation applies to these types of sewer accounts: 

• Residential accounts with connections to both water and sewer, and winter water usage greater than zero.

The residential volume-based rate structure is like a two-layered cake:

• The first layer is the volume charge, which comprises 30 percent of the total rate.  The volume charge is calculated by the average monthly winter water use per household based on specified winter months multiplied by 12 months to derive the annual use.   Average winter water use provides an accurate accounting of indoor water use and its impact to the District’s treatment facilities because outdoor irrigation should be off during the winter months. Thus, to maximize savings on your sewage bill, you should avoid using outside water sources during the specified winter months. This volume-based charge recovers costs to the sewage treatment and collection system that are affected by use and vary with the amount of sewage conveyed and treated.
• The second layer is the fixed charge, which comprises 70 percent of the total rate.  This fixed charge recovers costs that the sewage treatment and collection system incurs regardless of increased or decreased sewage into the system. 

City operated sanitation districts (including the cities of Cotati, Healdsburg, Petaluma, Rohnert Park, Santa Rosa, Sebastopol and the Town of Windsor) base rates partially on an estimate of  the amount of sewage generated by each household, based on water usage during  winter months. The 2010 District study found that such “volume-based” rate structures better account for household sewer discharge, promote water conservation, and provide financial reliability for District services. The study also found that volume-based rates would provide District ratepayers with the opportunity to control a portion of their sewage bill.

Residential Sanitation Rate Calculator – Single Family Dwellings

This calculator is only for Single family Dwellings in Sonoma Valley County Sanitation District's service area, not for multi-family or commercial because the number of Equivalent Standard Dwellings vary. 

Use this calculator to see how much you can save on your sewer bill by conserving water. The number of gallons must be greater than zero.

The formula for this calculation is $890.78 + (Gallons per month entered by user) X .00720 per gallon X 12 months = Your sanitation charge per year.

Press enter after entering amounts to view the Total Annual Sewer Bill

Reduce winter water use now to lower sewer bill

To maximize savings on your sewer bill, avoid outside water use during the winter months (for example, watering lawns and gardens, washing cars and hosing down driveways) and take advantage of District rebate programs.   Available rebate programs include:

High-Efficiency Toilet Direct Install Program

Questions on your Sewer Bill

For more information, please contact us.