An Integrated Model of Urban Water-Wastewater-Stormwater-Energy Systems

The urban water system is complex, comprised of water treatment and distribution, wastewater collection and treatment, and stormwater management (to avoid combined sewer overflow, flooding, and water quality permit violations). These components are often managed by separate agencies and companies, with their respective goals and budgets. In fact, they should all be working together towards the same overarching objective of urban water systems: to provide water to people and the economy for both indoor and outdoor uses at the lowest economic and energy costs and at the lowest achievable level of pollution.

We present an integrated model of urban water systems that accounts for changes in population, water consumption patterns, water saving technologies, raw water sources, water and wastewater treatment technologies, decentralization of wastewater treatment plants, water reuse demand, stormwater control measures, economic activities, electricity and other energy supply, landscape, weather, and climate. The methodological basis includes environmental life-cycle assessment (LCA) and life-cycle cost analysis (LCCA). The model is globally applicable. For effective decision making, we have created a decision making tool with an extensive, very detailed database to allow for specific, holistic analyses of the unique demographic, economic, and physical characteristics of urban areas.

The target audience for our model, tool, and results includes the government planners and regulators of the urban water system, water and wastewater agencies and companies, urban users of water (both individuals and companies), and real estate developers.

Through case studies of cities in different regions and climates over time, we show that water consumption does not have to follow population growth, in fact, it has dropped in many cities where the average per-person water consumption has been reduced due to water conservation measures. Water withdrawal and potable water production in some cities are more than four times more energy intensive than in others, and the energy intensity is expected to increase in many parts of the world due to droughts and overwhelmed water sources. Due to differing electricity mixes and corresponding greenhouse gas emissions, the average per-person water consumption in some cities is more than four times more impactful than in others, but reductions are feasible. Tailoring water quality to an application is a key to lowering energy and emissions. We show how we can diversify irrigation sources for agricultural production in and around cities, including the potential energy and emissions implications of wastewater recycling. Using the integrated decision support tool (i-DST), which allows for the comprehensive life-cycle cost and environmental assessment of gray, green, and hybrid stormwater control measures, we can estimate the needed investments in the gray and green infrastructure, and find that in areas with water scarcity, stromwater is a viable source of water.