1. Introduction
The availability of affordable clean water is one of the key technological, social, and economical challenges of the 21st century. Clean water, acknowledged as a basic human right by the United Nations [1], is still unavailable to one out of seven people worldwide. To complicate matters, increasing groundwater extraction around the globe results in progressive salt water ingress in wells and aquifers. As a consequence, there is a large interest in the development of economically attractive desalination technologies. Over the years, a number of desalination methods have been developed among which distillation, reverse osmosis, and electrodialysis are the most commonly known and widespread technologies [2]. A common goal for current research is to make these technologies more energy efficient and cost effective, both for the deionization of seawater and for brackish water. Considering that there is more brackish water than freshwater in the world, it is clear that it is particularly attractive to utilize the large brackish water resources for human consumption and residential use, agriculture, and industry.