4 Text work

1. drainage systems

5. arid regions

2. available water supply

6. humid regions

3. treated wastewater

7. natural precipitation

4. desalinated water

8. important advantages

1. Throughout the world, irrigation (water for agriculture, or growing crops) is probably the most important use of water,

a. without the irrigation of crop fields by water gotten from rivers, lakes, reservoirs, and wells.

2. Large-scale farming could not provide food for the world's large populations

b. but other, more efficient and mechanized methods are also used.

3. Pouring water on fields is still a common irrigation method today—

c. except for drinking and washing a smelly dog, perhaps.

4. One of the more popular mechanized methods is the center-pivot irrigation system,

d. where it replenishes water sources (water goes back into a stream or down into the ground) and can be used for other purposes.

5. When we use water in our home, or when an industry uses water, about 90 percent of the water used is eventually returned to the environment

e. which uses moving spray guns or dripping faucet heads on wheeled tubes that pivot around a central source of water.