The theme of this paper is that the desalination industry should modernize, recognizing that it is no longer a struggling, piecemeal effort, but a mature, large-scale enterprise, capable of using to the fullest the experience and technology that it has accumulated. In the early growth period many variations of design, process and materials were tried. Some were failures, but others worked well. The few well-performing designs have been copied many times over the years, with a tendency to resist all changes. In the meantime much has been learned. New processes and new materials have appeared, some early failures were found to have simple remedies, and some major economic relationships have changed. We now have the experience and scientific data to undertake a major-upgrade of desalination equipment and processes. We know that in many parts of the world desalination is not a temporary solution, but a permanent part of life. We can assess realistically the water needs, energy costs, environmental costs, and other aspects of a plant, and design the best, most efficient plant size and plant type for each location. When the water demand is large, we can now build a suitable large unit, instead of a multiplicity of small units. Ih this paper I will summarize some of the changed conditions that now govern optimum design, and some of the opportunities we now have to design improved, more efficient, and more reliable plants at much lower cost than existing plants. The recent design of a 75 mgd (283,000 m(3)/d) single unit vertical tube evaporator plant for the Metropolitan Water District of, Southern California (MWD) embodies many of the concepts discussed, and will serve as an example.