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How Sewer Service Charges Are Calculated

Revenues to operate the District are collected annually from residents and businesses that are connected to the sanitary sewer system. The following information explains how annual Sewer Service Charges are calculated and what steps businesses can take to minimize the charges.

Annual Sewer Service Charges are placed on  Alameda County property tax statements. The charges appear on the tax statement as a line item next to our contact number (510) 477-7626 and are listed as "Union Sewer Svc." Sewer Service Charges are not a property tax and are not related to the assessed value of a property. They represent a charge for a service provided, similar to your phone and P.G. & E. bills. The District includes annual charges on  property tax statements to save the administrative cost of generating and mailing our own invoices. More details on how the charges are calculated are provided below and on the Sample Sewer Service Charge Calculations page.

Residential Customers are charged at a flat rate

Charges for residential customers are based on a flat rate per dwelling unit. The current adopted rate (FY 2024: July 1, 2023 – June 30, 2024) per dwelling unit is $569.97 per year for a single family residence. 

Owners of multiple family residences such as an apartment complex will see charges of $502.28 for each dwelling unit. For example, a ten-unit apartment complex would be charged $502.28 per unit. $502.28 x 10 units = $5,022.80.

How water use is determined for Commercial & Industrial Charges

Charges for commercial and industrial customers are based on the volume and pollutant strength of the wastewater being treated. The volume of wastewater is determined from water meter records obtained from the Alameda County Water District. Credit is given for water used that is not discharged to the sanitary sewer, such as landscape irrigation. Due to the lead time involved to get yearly charges placed on the County property tax statements, the Sewer Service Charges on the current year's tax statement reflect services already provided. Water use for purposes of computing the service charge is measured from March of the previous year through February. The Sewer Service Charge for this period is then placed on the property tax statement that is mailed out in October, with the first installment due December 10th. The Sewer Service Charge Timing Chart below, illustrates when charges are collected.

Sewer Service Charge Timeline for Commercial and Industrial Users:












How pollutant strength is determined for Commercial and Industrial Charges

Pollutant strength is measured in samples of wastewater for two components: chemical oxygen demand (COD), and suspended solids (SS). Wastewater with high strength costs the District more to treat. For example, wastewater with high levels of suspended solids produces more sludge (a by-product of treatment). Sludge is treated and then disposed of at an agricultural site. If more sludge is produced, our hauling and disposal costs are higher. Therefore, rates are structured so that customers are charged based on the volume of solids they contribute to the system.

Wastewater strength for commercial and industrial customers is determined by one of three primary methods: General Assignment, Specific Assignment, and Direct Sampling

General Assignment: Most commercial and industrial customers, or properties that include several different types of businesses, are calculated by the General Assignment method. With this method, customers are assigned a general strength of strong, moderate or weak. The three rate components, VOLUME, COD, and SS are combined into one rate per 1,000 gallons of wastewater discharged. The current rates for Fiscal Year 2024 (as of July 1, 2023) are shown below:

  • Strong $15.71 per 1,000 gallons per year
  • Moderate $7.60 per 1,000 gallons per year
  • Weak $6.37 per 1,000 gallons per year

Specific Assignment: Strength values are based on studies of wastewater from similar types of businesses and represent an "average" for that group. The total charges under this method are the sum of three components - volume, COD, and SS. USD's current rates for restaurants are listed below:

  • Fast Food Restaurants $15.83 per 1,000 gallons per year
  • Full Service Restaurants $15.85 per 1,000 gallons per year

Direct Sampling: This method applies only to industrial customers with industrial discharge permits. Under this method, samples of wastewater are collected and sent to a laboratory for analysis. Both COD and SS are measured and then averaged with other samples taken that year to determine an average strength for use in calculating Sewer Service Charges. The sum of three components determines the total charge. The current rates for each component are:

  • Volume (Flow) = $3.74 per 1,000 gallons per year
  • COD = $424.91 per 1,000 pounds per year
  • SS = $1,140.90 per 1,000 pounds per year

For more details on how annual charges are calculated, see the Sample Sewer Service Charge Calculations for all three methods.

Renting or Leasing

Due to the lag in billing, commercial or industrial customers who rent or lease their property should carefully consider how Sewer Service Charges are addressed in the lease or rental agreement. Changes in tenants with different demands for water or that have different wastewater strengths will affect the yearly service charge. A landlord may not become aware of potential changes in service charges until well after tenant changes have occurred. All Sewer Service Charges are billed to the property owner. Property owners are responsible for paying the charges whether or not they are able to collect from their tenants.

Sewer Service Charge Ordinance 31.40 An ordinance providing for the establishment of sewer service charges for fiscal years 2021 through 2025. 



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5072 Benson Road

Union City, CA 94587-2508

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