The Water Cycle Only 3 percent of Earth’s water is fresh water. The atmosphere contains a small amount of fresh water in the form of water vapor, a gaseous form of water. Groundwater is water that fills the cracks and spaces in underground soil and rock layers.
The Water Cycle Water on Earth is naturally recycled through the water cycle. The water cycle is the continuous process by which water moves through the living and nonliving parts of the environment. In the water cycle, water moves from bodies of water, land, and living things on Earth’s surface to the atmosphere and back to Earth’s surface.
The water cycle includes three main processes: evaporation, condensation, and precipitation. Evaporation is the process by which a liquid changes to the gaseous state. Large amounts of water evaporate constantly from oceans, lakes, and rivers. A significant amount of water vapor is given off through the leaves of plants in a process called transpiration.
The Water Cycle Once evaporation occurs, warm air carries the water molecules high into the atmosphere. Higher up, the air tends to be much colder. Water vapor condenses into droplets, forming clouds. Water droplets in a cloud grow larger and eventually become so heave that they fall back to Earth. Water that falls to Earth as rain, snow, sleet, or hail is called precipitation.
The Water Cycle People use water for household purposes, agriculture, industry, transportation, and recreation. Irrigation is the process of supplying water to areas of land to make them suitable for growing crops. Water is essential for living things to grow, reproduce, and carry out other important processes.
Water on the Surface The water that flows over the ground is called a runoff. Tributaries are smaller streams and rivers that feed into a main river. A river and all its tributaries together make up a river system. The land area that supplies water to a river system is called a watershed. Ponds and lakes form when water collects in hollows and low-lying areas of land. A lake that stores water for people to use is called a reservoir.
The water trickles down between particles of soil through cracks and spaces in layers of rock. –Materials that allow water to pass through easily are called permeable. Materials that do not allow water to pass through are called impermeable.
The permeable layer that becomes filled with water is called the saturated zone. The level of the top of the water in the saturated zone is called the water table. The layer of rocks and soil above the water table is called the unsaturated zone. An aquifer is an underground layer of rock or sediment where water has collected.
Wetland Environments A wetland is an area of land that is covered with a shallow layer of water during some or all of the year. –Three common types of freshwater wetlands are marshes, swamps, and bogs. –Because of their sheltered waters and rich supply of nutrients, wetlands provide habitats for many living things. –Wetlands also help control floods by absorbing extra runoff from heavy rains.
Fresh Water Marsh Marshes generally are grassy.
Freshwater Swamp Swamps contain trees and shrubs.
Freshwater Bog Bogs are characterized by many types of mosses.
Water to Drink Water from both public and private supplies often needs some treatment to ensure that the water is safe and appealing to drink. –A measurement of substances in water besides water molecules is called water quality. –Appearance, odor, and taste are three factors that affect water quality. –The ph of water is a measurement of how acidic or basic it is on a scale (0-14). –The levels of two minerals, calcium and magnesium, in water is referred to hardness. –Another factor affecting water quality is the presence of disease-causing organisms.
Water to Drink The Environmental Protection Agency (EPA), has developed water-quality standards for drinking water that set the maximum concentrations for certain chemicals, minerals, and bacteria.
Water to Drink The first step is usually filtration, the process of passing water through a series of screens that allows the water through but not larger particles. –The second step involves the addition of a chemical that causes sticky globs, called flocs, to form. The next step is to chlorinate the water to kill disease-causing organisms. –Once treatment is complete, the water is distributed through an underground network of pipes called water mains.
Balancing Water Needs A water shortage occurs when there is too little water or too great a demand in an area – or both. A scarce of rainfall is known as a drought. Without precipitation to recharge the aquifer, the groundwater in the aquifer decreases. Reduce water needs, recycling water, and reusing water are three different form of water conservation by industries.
Freshwater Pollution The addition of any substance that has a negative effect on water or the living things that depend on the water is water pollution. The major sources of water pollution are human wastes, industrial wasters, agricultural chemicals, and runoff from roads. –Examples: pesticides, pollution in the air from factories causes acid rain. Runoff from roads include: gas, oil, and salt.