Long-Term Water Demand Forecasting for Sustainable Supply Planning

Tacoma Public Utilities (TPU), assisted by Raftelis Financial Consultants, completed a study to forecast water demand for use in financial and strategic planning. In order to better understand the sustainability of TPU’s facilities, the team developed a long-term water demand forecasting model. The model employed a multivariate regression to forecast daily water production through the use of social, economic, weather, and other independent variables over a 60 year timeframe. The model specification indicated that the strongest variables driving water demand included rainfall, temperature, and behavioral usage patterns. The forecasted water production volumes demonstrated a pattern of leveling off below highs seen in the 1990s. This forecast indicates that current storage and production facilities are likely to exceed the utility’s needs for at least the next 60 years. This information could lend support to plans for increasing wholesale water agreements with local enterprises even in years with high risk of drought.