Water Demand Forecasting Implementation: Best Practices for Improved Decision Making

North America's water and wastewater utilities have experienced many major changes in the past 20 years, but likely one of the largest has been the 'decoupling' of system demands from population growth. As populations in most communities have grown, water demands and dry weather sewer flows have decreased. This should be hailed as a major triumph of collaboration across North America between water utilities, regulators and fixture and appliance manufacturers, who have worked together to greatly improve the efficiency of water use in our homes and buildings. Unfortunately, the result has instead too often been hand-wringing about revenue shortfalls, concern over adverse impacts on drinking water quality or concerns for wastewater odor and corrosion. There has also been a reluctance to update engineering design standards, hydraulic models and utility master plans to reflect the new reality of lower per capita water use. Why do we seem to focus more on declining water demand as a problem than a major success story? How can we maximize the benefits and minimize challenges arising from changing water demands? In 2016, the Pacific Institute published a paper illustrating a large and consistent bias in water utility demand forecasts by large US water utilities over several decades and proposing a set of best practices to produce more reliable forecasts. In our experience, the historical tendency to over-predict future water demands is also common in Western Canada. Working with dozens of water and wastewater utilities, KWL has applied the Pacific Institute's advice to demand forecasting practices, enabling each community to tangibly benefit from their investments in water efficiency. The presentation will provide an overview of what we have learned and applied in our approach to water demand forecasting, using real-world examples from utilities serving 50 to 2 million customers that illustrate the benefits and applications of improved demand forecasting in utility management and decision-making. A good forecast begins with a good model of community water use. Key techniques that will be described include: 1)accounting for land use through sector and end use breakdown, 2)accounting for base and seasonal demand breakdown through land cover analysis, 3)estimating the impacts of climate change using climate models from the Pacific Climate Impacts Consortium, including the impacts of the 2021 Heat Dome event experienced by the Pacific Northwest, 4)evaluating population growth, economic uncertainty, and policy changes through scenario analysis, 5)incorporating non-revenue water in universally metered and unmetered systems, and 6)calibration and uncertainty assessment using Monte Carlo simulation. We will also focus on the issue of methodology implementation and methods for risk management when onboarding planning and engineering staff to transition from a previous, possibly overly simplified, forecasting methodology to a revised forecasting methodology, which applies best practices. Four real-world examples from Western Canada will be case studied to show how these forecasting techniques have enabled utilities of all sizes to: avoid or defer capital and operating costs of water supply and wastewater treatment, target specific sectors and end uses of water or wastewater with cost-effective demand management measures, establish effective seasonal watering restrictions that address water supply risks, set utility rates that encourage conservation while maintaining stable revenues; and establish design standards for efficiently sized future infrastructure, and evaluate system wide cost savings and benefits for the utility. Case Study 1: a mid-sized utility uses their demand forecast to support an evaluation of the risks for revenues with recent changes in population growth projections. Case Study 2: a large BC utility incorporates scenario analysis into their forecast to evaluate the implications for forecasting on timing for both a new water supply project and a chemically enhanced wastewater process system. Case Study 3: a large Alberta utility evaluates the benefits achieved by their water conservation program versus natural fixture replacement, alone. Case Study 4: the benefits of customer metering are evaluated by comparing demand forecasts for two mid-sized BC utilities one with universal metering and one without.