Many communities discharge sanitary wastewater to treatment plants in other communities. The communities receiving wastewater from neighbors need to find the best way of recovering, and even reducing, the costs of this service.

Infiltration and inflow (I/I), clean water entering the collection system, needlessly increases costs. When municipalities recover the cost of I/I without regard to its volume, contributing parties defer collection system maintenance, increasing costs for all wastewater customers. To foster more efficient use, wastewater systems need to accomplish the following:

  • Encourage contributors to reduce I/I costs by maintaining their wastewater collection systems.
  • Align each party’s incentives by allowing contributors to benefit from their own collection system improvements.

Identifying and Recovering Costs


Discovering how best to recover sewerage costs from participants does not have to be a mystery that only Sherlock Holmes could solve. The most sensible approach centers on matching costs with services provided.

Cost-recovery systems not based on volume give perverse incentives for increased I/I. Contributors save money by deferring or neglecting maintenance and replacement of wastewater infrastructure while the cost of treating I/I is spread across the whole system.

We can improve incentives by identifying I/I-related costs and allocating them based on measured I/I volumes. Even better, we can allocate costs according to contributors’ I/I during wet weather, when the treatment plant is near capacity and excess I/I causes the most harm.

Quantifying infiltration and inflow from each community stands out as crucial. If communities are charged simply based on the volume of water sold to them, then cost recovery does not account for the potentially enormous variation of I/I. For equitable operations and capital-cost recovery, communities should be charged based on what they contribute to sewerage, including I/I.

Measuring Infiltration and Inflow

This certainly begs the question of how to measure I/I. Many utilities are not currently set up to measure I/I, so what are these utilities supposed to do?

Ruekert & Mielke, Inc. (R/M) has developed a process to determine I/I between various locations by using water data, wastewater data, and GIS data. Through comparing the ratios of sanitary-sewer volumes to water-meter volumes between dry times and wet times, R/M identifies where and how much I/I occurs in a given group of communities within one sanitary sewer system.

Incorporating the I/I into a financial model, R/M allocates costs according to services provided to each community. That includes accounting for peak precipitation times. This approach not only provides an equitable pricing structure, but also appropriately signals the true cost of service to each community, encouraging the ones who contribute the most to reduce their I/I.

 To stamp CASE SOLVED on the mystery of cost recovery, contact an expert today.

About the Author

Edward F. Maxwell

Edward F. Maxwell
Financial Analyst

Edward joined Ruekert & Mielke, Inc. (R/M) in 2017 as a financial analyst. Before joining R/M, he worked in private-sector finance, analyzing capital investments, forecasting expenses and revenue, and crafting department budgets. At R/M, he creates financial solutions for all clients, from municipalities to corporate businesses.

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