Desalination: assessing efficiency A thermodynamic framework enables comparison of different desalination plants and processes. Desalination of seawater is a key process for meeting the worlds growing need for potable water, enabled by substantial increases in efficiency of the process of over the last few decades. Now, Kim Choon Ng and colleagues from King Abdullah University of Science & Technology argue that the grade of input energy used during desalination, defined by how the energy is generated, must be considered when determining the efficiency of desalination plants. They define a metric to assess process efficiency, suggesting that the majority of desalination processes are operating below the ideal thermodynamic limit.