A fourth characteristic is that water expands when it freezes. Most substances shrink when they change from liquid to a solid, but water gets bigger. As a result, ice is less dense than water and floats on top of the surface. Ice on the surface of the Arctic Ocean acts as a protective layer that allows sea life to thrive underneath. The solid surface allows other species such as polar bears and humans ease of travel. Holes in the ice where seals and whales would come to the surface to breathe are popular hunting sites. The fifth characteristic of water is its capacity to store heat. Large amounts of heat energy are needed to raise the temperature of water. Therefore, water stores a lot of heat in the summer, which it radiates back into the air during the winter. This moderates the temperature of the Earth and keeps it from changing too drastically. It also makes water pleasant for recreation in the summer. Many people are attracted to the shores of lakes and oceans because they offer a relief from hot summer temperatures further inland. These five properties of water make it extremely useful, but also contribute to many abuses. Water is so useful that many of the different uses have to compete with each other, or may even conflict with one another. For example, if water is withdrawn from a river to irrigate crops, then it is no longer available for drinking water or to produce hydro electricity. The challenge is to balance the many ways water is used and to avoid misusing it. How Humans Use Water There are two main ways that human beings use water. Many water needs do not require withdrawing it from a river, stream, lake, or ocean. Recreational uses such as swimming and surfing, fishing, shipping, and the production of hydroelectricity are called non-withdrawal uses . Non-withdrawal uses can usually
Lesson 8, page 8 Canadian and World Issues CGW4U-A Copyright © 2007 The Ontario Educational Communications Authority. All rights reserved. coexist with one another. When conflicts occur, it is usually possible to find solutions without too much difficulty. For example, when hydro facilities disrupt movements of migrating fish, it is usually possible to solve the problem by using fish ladders that allow fish to migrate around the dam. Other uses of water require withdrawal of water and are known as consumptive uses . Consumptive uses compete with each other for the right to withdraw water. The graph in Figure 8.4 shows how fresh water has been consumed worldwide from 1900 to 2000.The most common consumptive use of water worldwide is for growing food. Agriculture consumes more than 3000 cubic kilometres globally each year. For thousands of years, humans have been pouring water onto crops and feeding livestock with water. If there are water shortages, there will be food shortages. The graph shows that industry consumes the second-largest quantity of water. The quantity of water used by industry has increased a great deal since around 1960. Regionally, there are differences in the way water is consumed. According to the World Resources Institute (WRI), countries in the less-developed world use more water primarily for agriculture. In Asia, farming
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