The sewer service charge for a non-residential customer is calculated individually based upon the volume and strength of the customer's sewage measured in Equivalent Dwelling Units (EDUs) multiplied by the annual sewer service charge rate in effect. The current sewer service charge is $388 per EDU per year. EDUs are based on the customer's annualized water usage (in units of 100-cubic feet of water) multiplied by the customer's strength factor (contact the District for your strength factor). The formula to calculate your annual charge is shown below.

(Annualized Water Usage* x Strength Factor = EDU) x $388** = Annual charge.

* Water units are calculated by averaging the June/July and Dec/Jan water usage from your Marin Municipal Water District water bills and dividing by the gallon per day conversion factor of 14.64***

**Strength and Loading Factors. The strength is based on domestic wastewater produced by residential customers. The residential strength factor is the standard against which higher strength commercial and industrial sewage discharges is measured. Thus, the loading factor for residential customers is considered 1.0. Each non-residential (business/commercial) customer’s premises is assigned a loading factor, which represents the strength characteristics of the wastewater discharged by the premises. The loading factors are:

If the District determines that these loadings do not accurately represent the strength characteristics of the wastewater discharge from a particular property, (for example, mixed use occupancies), the District establishes a loading factor which represents the actual conditions.

^***  Conversion Factor:  The figure “14.64” normalizes a business’s average two month water usage to that which is discharged from a typical single family residence. Its derivation is as follows:

            180 gallons  _x    1 cu. ft    _x   365 days   x   2 months x   1 unit       =  14.64.

                 day             7.48 gal        12 mos.                         100 cu ft. 

Businesses in the City of Sausalito are charged an additional amount for sewer collection system maintenance and repairs in the city. Contact the city for details about this charge.

Note that businesses in unincorporated areas also pay an additional amount for the repair and maintenance of their wastewater collection pipelines. The charge is $50.66 per EDU per year.