Water Issues - Water Availability, Water Suitability, Where Water Is Power—international Water Wars?, Ocean Protection, Drinking Water

Water is precious for many reasons. It is an essential resource for sustaining human, animal, and vegetative life. A living cell is mostly water. An adult human's body is about 65 percent water; blood is 90 percent water. Agriculture is absolutely dependent on water to produce food crops and livestock. Water is crucial to tourism, navigation, and industry. Enormous amounts are used to generate power, mine materials, and produce goods. Water is an ingredient, a medium, and a means of conveyance or cooling in most industrial processes. Water supplies a vital habitat for many of Earth's creatures, from the whale to the tadpole. There are entire ecosystems that are water-based.

All of these competing uses put an enormous strain on Earth's water supply. Overall, the amount of water on Earth remains constant, simply passing from one stage to another in a circular pattern known as the hydrologic cycle. Water in the atmosphere condenses and falls to Earth as precipitation, such as rain, sleet, or snow. Precipitation seeps into the ground, saturating the soil and refilling underground aquifers; it is drawn from the soil by vegetation for growth and returned into the air by plant leaves through the process of transpiration; and some precipitation flows into surface waters such as rivers, streams, lakes, wetlands, and oceans. Moisture evaporates from surface water back into the atmosphere to repeat the cycle. (See Figure 6.1.)

Humans have interrupted the cycle to accommodate the many water demands of modern life. Flowing rivers and streams are dammed up. Groundwater and surface water are pumped from their sources to other places. Water is either consumed or discharged back to the environment, usually not in the same condition. Water quality becomes increasingly important. There are two primary issues when it comes to water—availability and suitability.