Water Is Life

Questions to Consider

• What is water, and why is water important?

• What are the special properties of water, and why are they important?

• What is the hydrosphere, and what is its importance to life on Earth?

• How do we use water? How much water is available for human use?

• What are natural resources? What are aquatic resources?

• What is conservation? Why is it important?

• How can we tell if water is polluted or clean? How does water pollution affect aquatic life?

• How does the temperature of water affect the amount of oxygen in it?

• What is water quality? How do humans affect water quality?

CHALLENGE QUESTION

What is the source of your drinking water? Are there any water quality or water quantity issues about your water source? What will affect your water source in the future? Who makes decisions that affect your water source?

Did you know that plants and animals are made up mostly of water (fig. 1.1)? Humans need clean water to keep them healthy. Without drinking water you would die in about one week. Our need for water links us to the past and to other living creatures. Since ancient times, societies have succeeded or failed according to their ability to get clean water and protect it for future use. Today's modern cities still depend on water for everything from flushing toilets, to fighting fires, to building the cars we drive. Your community depends on water, too. Using water wisely is critical to our survival. Water sustains life on Earth. Life is impossible without water.

What Is So Special about Water?

Water is made up of molecules that have two hydrogen atoms and one oxygen atom joined together (fig. 1.2), so we also call water H2O (pronounced "h-two-oh"). Water can take three forms: liquid, solid (ice), and gas (vapor). Water exists in all three forms on Earth.

Water can travel great distances. For example, clouds are made up of tiny ice crystals and water droplets. Water can move up plant stems, keep animals and plants alive, break rocks, and dissolve or erode almost anything. The chemical structure of water gives it these amazing powers. Water molecules attract one another in a way that makes them form drops. Have you ever watched raindrops creep across a window? When the droplets get close to each other, they join to form one larger drop. Water molecules cling to other things, too. This ability to cling allows water to move up plant roots and enables blood to flow through tiny blood vessels. It also enables bugs and other small things to rest on the surface of water without sinking (fig. 1.3).

Water boils at 212 °F (100 °C) and freezes at 32 °F (0 °C). Water can absorb a lot of heat before its temperature begins to rise. A large body of water heats up very slowly, and it cools down just as slowly. This property allows living things to survive in water's fairly constant environment. Water is unusual because its solid form (ice) is not as dense as its liquid form. This explains why ice forms at the top of a lake, floating on the unfrozen water below it and insulating aquatic organisms from extreme temperatures. Without this property, lakes would freeze solid throughout, trapping and killing fish and other aquatic life.

Chemists call water the "universal solvent" because it is very good at dissolving many different things. Seasonal cycles of rainfall and flooding have shaped many landscapes through erosion (fig. 1.4). Because of these properties, water in nature is never completely pure. This also means most of the chemistry of life happens in solutions of water. For example, blood is really just a lot of our cells contained in water! Water also contains dissolved oxygen and other gases from the air, dissolved minerals from the Earth, and organic matter that supply essential elements and nutrients needed by aquatic organisms to live and grow underwater. Unfortunately, the gases, minerals, and other things that water dissolves can also pollute it. Water pollution occurs when there are too many natural or human-made substances of a harmful nature in the water. These substances can harm or kill the plants and animals that live in or near the polluted water.

How Much Water Is There?

At this moment, the Earth has all the water it has ever had or will ever have. Our planet will get no new water. The good news is that water is rarely ever destroyed. Earth's water is continually being recycled through the hydrologic cycle. From wetlands, oceans, and lakes, water evaporates into the atmosphere as water vapor and then falls back to Earth as rain. Water cannot be made in a factory.

The hydrosphere is all the water on Earth. Water covers about 71% of the Earth's surface. That is about 358 quintillion (358,000,000,000,000,000,000) gallons of water! But 97% of the world's water is ocean water, which is saltwater and too salty for humans to drink. That leaves only 3% of the water as freshwater to supply the whole world. Yet most of that freshwater, about 80%, is frozen in the polar ice caps. Most of the rest of the freshwater is too polluted to use, is trapped in soil, or is just too hard to get (fig. 1.5). That leaves us with just one-half of one percent of the world's freshwater to use. As the world's population grows, the demand for freshwater grows. Luckily, water is also one of the most recyclable substances on Earth. In fact, all the water on the planet has been recycled countless times—we drink the same water the dinosaurs drank! So when we use water, we do not destroy it or make it disappear. We may move it. We may make it unusable for drinking purposes, sometimes for a short period or longer if water becomes polluted with harmful contaminants. The more polluted it becomes, the more difficult it may become to clean it. But eventually water is recycled.

A person can live on a gallon of water a day for drinking, cooking, and washing. But most people in Texas use far more than this. On average, every American uses about 90 gallons of water each day. Worldwide the need for water has tripled over the past 50 years. To get this water, people have drained rivers dry, turned grand valleys into huge tubs of water, and pumped so much water out of the ground that the Earth's surface has sunk beneath our feet. In the United States, we often take for granted the clean water that flows out of our faucets. We can assume our water is safe. We do not think much about where it comes from, how the water is cleaned and distributed, how much we use each day, or what happens to it when we flush our...