**Abstract**

As well known, the basic birthrights of human are the clean air, clean water, healthy food, and green energy. So, clean water is the second important requested need of all living organisms on Earth. To know the importance of water to our human bodies, a deficiency of just 2% in our body's water supply indicates dehydration. Nowadays, all countries suffer from the problem of freshwater shortage. Despite the importance of clean water for our lives, only 0.01% is available as surface water such as the rivers, lakes, and swamps. These frightening facts have made it a national and humanitarian duty for scientists to research how to overcome the water problem and how to provide alternative sources of safe drinking water using renewable energies. Desalination is the most famous and operative technique used to overcome this problem. In this chapter, the different desalination techniques are reviewed and reported. Also, the solar distillation processes are mentioned with an extended review on the solar distillers. Besides, the application of artificial intelligence in improving the performance of desalination systems is reported. The main conclusions are stated at the end of this chapter.

**Keywords:** desalination, thermal desalination processes, stage flash, reverse osmosis, solar distiller

### **1. Introduction**

Any human being needs the water as the second most important fluid after air to be able to live on the Earth. Actually, around two-thirds of the Earth is covered by water (~ 71%), but more than 7% of this water cannot be used because they are in the form of ocean, ice caps, glaciers, ground, and aquifers [1]. Therefore, the freshwater that is available to use by the people is only around 1% all over the globe. So, the need for desalinated freshwater arises day by day [2]. In addition, the applications of freshwater such as cooking, drinking, and farming make it in a difficult situation. As a result, providing safe drinking water is a major challenge all over the world [3, 4]. The predicted freshwater shortage problem in 2030 is illustrated in **Figure 1**.

The simplest well-known cycle for the water is the hydrological cycle, which had sequentially the steps of water surface evaporation, condensation, cloud creation, runoff, and rain. So, the water controls the ecosystem of any society [6, 7]. This is because the potable water shortage is a problem of both the remote and urban communities [8].

*Estimated global water scarcity in 2030 [5].*

#### **Figure 2.**

*Capacity of distillation processes for (a) the globe, (b) USA, an (c) Middle East countries in 2002 [16].*

The thermal desalination processes follow the same principles of the natural hydrological cycle, but they use huge energy amounts. Distillation is accomplished by introducing saltwater into the process, which produces two output streams: one of freshwater and the other of brine water. Distillation of seawater produces freshwater [9–13].

Distillation becomes a key source of freshwater for most of the world's regions. Because of the ample water, the distillation procedure is mostly considered in coastal places. The most significant feature of this procedure is that it is completely safe for everyone involved—in other words, it has no negative consequences for the environment [14]. According to a survey conducted in the preceding decade, roughly 75 million people around the world rely on distillation for their everyday requirements. Distillation is the only source of freshwater for many countries. Saudi Arabia, the United States, the United Arab Emirates, Spain, and Kuwait are the top five countries in terms of desalination plant capacity, with 17.4, 16.2, 14.7, 6.4, and 5.8%, respectively [15]. The capacity of distillation processes for various countries is depicted in **Figure 2**; for (a) the globe, (b) USA, and (c) Middle East countries in 2002.

Till 2015, the total capacity of desalinated freshwater is 86.55 million cubic meter a day, which were obtained from around 18,000 plants for desalination around the globe. The Middle East and North Africa account for almost 44% of the above total capacity. Over the last 20 years, 80% of the energy utilized for freshwater producing has been lowered because of contemporary advancements in distillation technologies [16].

*Thermal Desalination Systems: From Traditionality to Modernity and Development DOI: http://dx.doi.org/10.5772/intechopen.101128*
