Desalination and Long-Haul Water Transfer: A Case Study of the Energy-Water Nexus in Texas

Abstract

Energy and water are interrelated. We use water for energy, for example to cool thermoelectric power generation and produce liquid fuels. Conversely, we use energy for the collection, treatment, disinfection, and distribution of water and wastewater. In the water sector, strain on existing water supplies, population growth, and the push toward stricter water and wastewater treatment standards potentially leads to more energy-intensive water. Treating water to more stringent potable standards requires additional energy beyond conventional treatment. Additionally, as existing water supplies become increasingly strained in some locations, water planners turn to alternative options to quench cities’ thirst. Among these options for inland cities is desalination of seawater followed by long-haul water transfer. Though many desalination technologies exist to treat seawater to potable standards, reverse osmosis membranes are the most common technology in use because of their cost-effectiveness and productivity as compared with more traditional techniques such as multi-effect distillation. [1] However, the high pressures required for reverse osmosis make desalination a very energy-intensive water supply option. The subsequent conveyance of desalinated water through long-haul pipelines also requires large amounts of energy. Even for local water production, 85% of the energy required for standard surface water treatment goes toward water distribution, and so adding in long-haul will only increase this requirement. [2] To examine desalination and long-haul transfer as a drinking water supply option, Texas was chosen as a test-bed with desalination near Houston and long-haul transfer to the rapidly-growing Dallas-Fort Worth metroplex. Various pipeline routes were modeled to simulate options for long-haul desalinated water transfer. Elevation change over the route of the long-haul transfer pipeline was determined using a digital elevation model of the state of Texas. These elevation data were then used to calculate energy requirements for water pumping with standard assumptions for pump performance, efficiency, and rating. Combining these energy requirements with the energy demands for desalination provides an estimate of this option as a water supply for Dallas-Fort Worth. Results suggest that desalination and long-haul transfer as a drinking water supply is 9 to 23 times more energy-intensive per unit of water than conventional treatment of local surface water sources, an increase of 230 to 630 megawatt-hours per day for 20 million gallons. Ensuring adequate water supplies for the future is important, as is developing these water supplies in a sustainable manner. The energy-intensity of desalination and long-haul transfer as a drinking water supply suggests this option is not a sustainable water or energy policy decision if other less energy-intensive options exist.