13 A2 water vital for life

CHAPTER 1 Water in Our Lives PEOPLE USE A LOT OF WATER EVERY DAY. HOW MUCH DO YOU USE? A person can live without food for more than a month. Without water, a person dies in less than one week. We need water inside our bodies. We need water outside our bodies, too. We need to wash our clothes, our dishes, our food, and our bodies. A person can easily use seven and a half liters of water a day to brush his teeth. We also need water to make food. It takes three and a half liters of water to process the meat for one hamburger.

We even need water for the cars we drive. It takes 7,843 liters of water to make four new tires for a car. Not everyone uses the same amount of water, however. The average person in the United States uses 2,500,000 liters every year. That's the same as an Olympic swimming pool! Someone in China uses about 700,000 liters in a year. People in Uganda or Ethiopia use about 5,000. One reason for this big difference is the way people use water. Do you leave the water running when you brush your teeth? That's about 11 liters per minute. Do you take a shower or a bath? A five-minute shower uses about 75 liters of water. A full bathtub can hold 130 liters. Do you wash your car in the sunshine, or do you wait until it rains?

CHAPTER 2 Water in the Air SOMETIMES WE CAN SEE WATER IN THE AIR- AND SOMETIMES WE CANT: There is a lot of water in the air. Think of clouds, for example. A cloud is a group of very small drops of water. The drops are so small that they float in the air. There are different kinds of clouds. Cumulus clouds are big and fluffy. Cirrus clouds are very thin and long. When cirrus clouds are in the sky, it means the weather is going to change soon. Cumulus and cirrus clouds are white. They are white because the drops of water are not very close together. Gray clouds have more water, and the drops are very close together. These are rain clouds, or nimbostratus clouds.

Fog is also a cloud. But it is not up in the sky. It is down on the ground where we walk. Fog can be beautiful, but it can also be scary. Fog stops you from seeing or hearing things well, so most people don't feel safe when it's very foggy. That's why there is often a lot of fog in scary movies. London is famous for its fog. In old movies with detectives like Sherlock Holmes, the streets of London are often full of fog. But that wasn't really fog. It was smog! When fog mixes with smoke in the air, it makes smog. Smog isn't healthy for people to breathe. Today, there isn't as much smog in London as there was in the days of Sherlock Holmes. The air is much cleaner, but it's still often foggy in London.

Humidity means how much water is in the air. On a humid summer day, the skin on your arms, face, and legs feels wet. It's hard to breathe because the air feels heavy. Your clothes stick to your body, and you feel uncomfortable. When the weather is humid, the temperature usually feels higher than it really is. Think about this: when the air temperature is 24C and there is 0 percent humidity, it feels like 21C to our bodies. But if the humidity is 100 percent, it feels like 27C. That's why you feel more comfortable in a warm, dry place than in a warm, humid place.

Of course, water can also be in the air in the form of rain. When the tiny drops of water in the air come together, they get big and heavy and make clouds. When the drops become too heavy, they fall from the clouds as rain. If it rains too much rain in one place, then a flood can happen. The water from rivers goes onto fields, into towns, and into buildings. But there are good floods and bad floods. Good floods can help farmers. The flood waters can bring new richer soil into the fields. That means it's easier for the farmers to grow crops. Bad floods can kill people and destroy homes. In October 2011, there was a very bad flood in Thailand. As many as 800 people died, and tens of thousands of people lost their homes.