Water for Life

Kathleen Damonte

It often seems to rain endlessly in spring. Although rainy days are a nuisance, they are actually vitally important to all living things. Rain showers are part of the continuous movement of water between Earth’s surface and the atmosphere that is called the water cycle. The following will introduce you to the importance of water and the basics of the water cycle.

Water is an essential nutrient for all living things. A person can only survive for about a week without water. Water helps transport oxygen and other nutrients throughout the body, aids in digestion, cushions joints and tissues, and helps maintain body temperature. People need fresh drinking water but cannot produce it themselves.

Learning about the water cycle will help you understand how the water that humans depend on is continuously replenished.

The water we drink is a liquid. Water can also be a solid or a gas. Ice and snow are solid forms of water. Water changes to an invisible gas called water vapor when the temperature increases. This process is called evaporation. Puddles evaporate after it rains.

When water vapor cools it turns back into liquid water through a process called condensation. Water that collects on the outside of a glass of ice-cold lemonade in the summer has condensed from the air. Where does that water come from? Young children often believe the glass is leaking. Older children can understand that the air on the outside of the glass has water vapor in it. When it hits the colder cup, it condenses.

How the Water Cycle Works

In the water cycle, water moves from Earth to the air and back to the land. Heat from the sun causes water to evaporate from the land and ocean. As water vapor rises it meets cooler air and condenses into water droplets. The droplets collect around small pieces of dust in the air and form clouds. Given the right conditions, water droplets in the clouds eventually fall back to the ground or ocean in the form of rain, snow, or hail. This process is called precipitation.

Water then accumulates (collects) in streams, in ponds or lakes, in the soil, in the ocean, and even in puddles on the playground. Some of this is the fresh drinking water that humans need. This accumulated water eventually evaporates and starts the whole cycle over again. The amount of water in the world always remains the same, it just gets recycled over and over again.

Now use the water cycle to help germinate some seeds in a miniature terrarium. In the terrarium, water will continuously evaporate, condense into droplets, precipitate down the side, and accumulate in the soil.

Kathleen Damonte is a middle school science teacher in the Montgomery County Public School System in Maryland.

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