how many people on earth lack access to clean, fresh water?

Water - The Most Important Liquid on Earth

Water is the most important liquid we know. It is everywhere we look. Water is in the ground and in the air that we breathe . All animals, plants and humans need water to survive . Water has formed our earth since its beginning. It also prevents the earth from becoming too hot or too cold. Water never disappears . We use the same water over and over again.

Chemistry of water

Water consists of very small molecules. Each of them has two hydrogen atoms and one oxygen atom. The chemical formula of water is H20.

Water can be a solid , a liquid or a gas, depending on the temperature it has. At 32° F (0° C) water freezes and turns into ice. It expands and becomes lighter. As a result ice floats on water. That is why you should let water out of pipes during the wintertime because it may freeze and burst the pipes. At 212°F (100°C) water boils and escapes as a vapour into the air. Between these two states water is a liquid. Most of the world's water is in liquid form. It can be found everywhere on earth.

Water molecules always move. In ice they are very far apart from each other. They move very slowly or often not at all. Molecules in water vapour move very quickly.

Water in our daily lives

Water has been important for people for thousands of years. Without water there would be no life on earth.

We use water in our houses for cooking, bathing and washing the dishes. Water is used to grow food. In many dry areas farmers must bring water to the fields through canals and expensive irrigation systems .

Industries and factories also use water. Fruits and vegetables must be cleaned before they can be processed and sold in supermarkets. Water is used for cooling in many areas, for example in steel production.

Many countries around the world use water to produce energy. Power stations burn coal which turns water into steam. Countries with many mountains and rivers use the power of water to produce electricity .

Water is important for our free time. People enjoy themselves at seaside resorts or on cruise trips .

Transportation was at first carried out on waterways . Ancient civilizations traded goods across the Mediterranean Sea . Today oil, coal, wheat and other products are transported on waterways.

Water and the human body

The human body is made up largely of water. Up to 75% of our body is water. Water helps us digest food. Chemical reactions in our body would not be possible without water. It also needs water to help carry away the substances that we do not need any more. Water regulates our body temperature so that it always stays the same. Although we can live without food for a few weeks without water we would die within a few days. A normal human needs about 2 to 3 litres of water a day to survive .

World water supply

The amount of water we have on earth is always the same . However, clean water, is getting rarer because of pollution .

Most of the world's water, about 97% is in the oceans. 1.4 billion cubic kilometres is saltwater. Only 3% is the freshwater in lakes, rivers and glaciers.

Much of the world has enough fresh water but there are regions that are too dry and don't get enough rain. Developing countries often do not have enough water for their growing populations . Other areas do not have enough water because people waste it.

Water cycle

Water moves in a steady cycle. It never goes away or disappears but it changes from solid to liquid to gas.

When the sun heats up water it becomes a gas and evaporates . As it rises it cools down and clouds form. Clouds have many very small droplets of water in them. When they get too heavy they fall down to the ground as rain or snow.

Although some of this precipitation rises directly into the atmosphere again most of it gets into the ground and remains in aquifers . Snow and ice remain on glaciers and ice caps until it gets warmer. Then it starts melting and the liquid follows into lakes and rivers.

Water has shaped the surface of the earth for many years. It causes erosion , makes mountains smoother , rivers carve themselves into valleys and makes them wider . Ocean waves form coastlines .

Water Treatment

Not all water is safe to drink or to take a bath in. Some of it needs to be cleaned or purified before we can use or drink it. This is done in three basic steps:

Water first flows through a basin which has chemicals in it . The bacteria , mud and other dirty substances that are in the water stick to these chemicals and move down to the bottom of the basin.
Water then goes through a filter made up of sand and gravel . Other particles are filtered out.
In the last phase chlorine is added to the water. It kills the bacteria that somehow get through.

Dirty, used water is carried away through sewage systems . It often smells bad and has a lot of bacteria in it. Most cities have treatment plants that turn used water into clean water that can be used to irrigate fields.

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Words

although = while
ancient = old
apart = away
aquifer = underground layer of water
atmosphere = the mixture of gases that is around the earth
bacteria = very small living things, some of which cause illnesses and diseases
basic = main, important
basin = very big, round container
billion = a thousand million
blood stream = tubes in your body through which blood passes
boil = when a liquid becomes hot and turns into gas
breathe = to take air in through your lungs
burst = split open, break apart
carry away = take away
carry out = to do something
carve = cut
chemical reaction = chemicals mix and change into new materials
chlorine = a greenish-yellow gas with a strong smell; it is used to keep water in swimming pools clean
coal = a hard black mineral that you dig out of the ground and burn to produce heat
coastline = where the sea meets land
consist of = is made up of
constipation = it you have problems getting rid of the solid waste from your body
cruise = holiday journey by boat
depend = affected by
developing countries = a poor country that is trying to make its economy grow
digest = to change food that you have eaten into substances your body can use
disappear = go away
dissolve = to mix with a liquid and become part of it
droplet = very small drop
electricity = the power that is in cables or wires ; it gives us light, heat and makes machines work
erosion = when rock or soil is destroyed by wind, rain or the sea
escape = get away
evaporate = liquid changes into gas
expand = grow or get bigger
float = drift, swim
flow = run through
flush =wash out
freshwater = water from rivers and lakes
glacier = large mass of ice that moves slowly down a mountain valley
goods = products
gravel = small stones
humans = people
hydrogen = the lightest of all gases; it forms water when combined with oxygen
ice cap = an area of thick ice that covers the earth's poles
irrigate = to bring water onto fields
largely = mostly
liquid = a watery substance
lubricate = to make something move more smoothly
Mediterranean Sea = sea between Europe and Africa
melt = to turn from solid into liquid
mud = wet, sticky earth
nutrient = a chemical or food that gives plants and animals what they need to grow
oxygen = a gas that has no colour or smell; it is in the air that we breathe
particle = very small piece of something
pipe = a tube through which gas or a liquid flows
plant = place where something happens
pollution = the process of making air and water dirty
population = the people that live in a country
power station = building where electricity and energy is produced
precipitation = rain or snow that falls onto the ground
prevent = to stop something from happening
process = to make food better by adding chemicals to it
protect = defend
purify = to make clean
rare = not found very often
regulate = control
remain = stay
seaside resort = holiday towns near the coast
sewage system = waste from the human body together with water that is carried away from houses through pipes
shape = form
smooth = round, flat
solid = an object that has a fixed shape, not a gas or a liquid
steady = stable, always the same
steam = the hot gas that water produces when you boil it
steel = strong metal made out of iron
stick to = fix, glue, attach
store = keep, save
substance = material
surface = the top layer of
survive = to live on
tissue = the material that forms cells
used = not new
valley = lower land between two mountains , usually with a river flowing in-between
vapor = gas
waste = material that you cannot use and do not need any more
waste = to throw something away even if you can still use it
water treatment plant = place where dirty water is cleaned
water vapor = water in the form of small drops in the air
waterway = places where boats travel
wheat = plant that you make white bread from