Brackish vs. Seawater Desalination: Which Is More Cost-Effective?

Both brackish water desalination and seawater desalination processes are well established and are commonly used around the globe to create new water supply sources. The farther the source water is located from the ocean or seashore, the lower the salinity (TDS) of the water and the lower the osmotic pressure that needs to be overcome when producing desalinated water. This is one of the major reasons that brackish desalination is often considered less costly that seawater desalination. Based on a number of project considerations, however, seawater desalination can be beneficial and more cost-effective than brackish water desalination. To make a fair comparison, we need to properly compare all major aspects of both types of projects to define the best and most appropriate desalination technology. While brackish water has less feed water TDS, it is more challenging to dispose of the produced concentrate. Also, although brackish water desalination needs less energy to overcome osmotic pressure, it usually requires more energy to draw the water from the well than it takes to pump seawater from the open ocean intake. Another aspect is that the temperature of the brackish well water may be lower than the temperature of ocean water, giving seawater desalination an advantage in energy demand. In comparing brackish to seawater desalination, the major aspects to evaluate are the following: 1) Locations of seawater and brackish water plants, relative to the location of major consumers of the desalinated water, 2) Transportation (pumping and disposal) costs of the feed water and produced water, 3) Potential collocation of a seawater plant with a large industrial user of the seawater for cooling or other purposes (such as a power plant), 4) Produced quality of brackish water and seawater desalination in terms of the major minerals and emerging contaminants, 5) Sustainability of the water source: capacity and depth of the brackish water wells, type of the soil, 6) Technical and economic aspects of produced concentrate disposal, 7) Costs of the permitting processes for brackish and seawater desalination, and 8) Economics of both brackish and seawater desalination treatment processes: capital costs, operational and maintenance (O&M) costs, and lifetime water cost — Total Water Cost (TWC). This paper discusses the major evaluation criteria and considerations needed to properly compare brackish vs. sea water desalination to determine the economic and technical aspects of the more favorable desalination technology for a given desalination project.