Читать книгу Introduction to Desalination - Louis Theodore - Страница 12

The title of this book includes the word desalination. Dictionary.com (2012) defines desalination as “the process of removing salt, esp from seawater so that it can be used for drinking or irrigation.” Thus, desalination is a process that produces potable water. The reader should keep in mind, and this will be discussed later in the book, that there are other processes available for producing potable water, many of which are currently uneconomical. For this reason, the book primarily deals with desalination. The general topic of potable water is also considered and is addressed in several of the paragraphs to follow.

The world’s total water is enormous compared with the presently conceivable needs of man, yet there is a growing water problem. Of the 1.39 billion km³ (332 million mi³) of water in the Earth’s crust 99% is salty and useful neither for irrigation by present techniques nor for the majority of man’s other needs.

Rain provides many times the world’s annual water needs, but fresh water supplies vary widely over the Earth and from time to time in a given region. This accounts for the “water problem” that exists as the Earth’s population continues to grow. In the United States, the actual “consumptive use” is approximately 12%–18% of the potential supply. Water prices are low, and on a statistical basis there should be no water shortages for many years. These average figures are of little comfort to the people of arid regions, however, and the United States, though relatively well supplied with water, is now beginning to turn to sources other than rainfall and runoff to meet growing water demands. The Southwest has too little water to support rapid population expansion. California has embarked on multi-billion dollar projects to bring water nearly 800 miles to Los Angeles and southern California from the wetter northern parts of the state. Outside of the United States, expensive desalination plants have been in operation for many years in the Virgin Islands, many Persian Gulf states, the West Indies, Libya, South Africa, and Israel.

An obvious way to increase water availability is to recover fresh water from seawater or large underground stores of brackish water that are available in many arid regions, but that are generally not usable without significant treatment. Other options for increasing potable water supplies is to find ways to use the saline or brackish water for agriculture or other uses that can tolerate higher salinity levels, or to actively pursue water conservation measures to protect limited fresh water supplies that may be available.

This chapter introduces the reader to the general subject of global water supplies and water scarcity issues through a review of water availability and water sources, global water resources, global water resource issues, and the history of desalination. A series of illustrative examples are provided to highlight concepts presented throughout the chapter.