Drinking water is essential for all life on Earth. With daily use, the growth of industry and rising standards, the demand for water is increasing. This is especially true in areas where there are no abundant natural sources of drinking water. One of the solutions to this problem is the construction and improvement of desalination plants, of which there are more and more both in the world and in Europe. The main purpose of desalination is to turn salty seawater into drinking water. This paper presents the countries and geographical areas with the largest number of desalination plants. The focus is on thermal desalination processes. They are most commonly used in countries with available energy sources such as the Middle East. The development of the technology aims to achieve the highest possible efficiency while reducing costs at the same time, as desalination processes are expensive from an energy point of view. Thermal processes are based on distillation processes, i.e. the physical change of water phases. Various distillation processes are presented and their advantages and disadvantages are listed. The aim of thermal desalination plants is to recover water in a usable form, namely clean drinking water, from various sources of unusable water.