Water, water, everywhere, but not much to drink! Listen to Notes.(right click, choose "open in New Tab".)
The most common element in the Universe is hydrogen. Hydrogen is one of the 93 natural elements that make up all matter in the Universe. On Earth, pure hydrogen is a gas and because hydrogen gas is less dense than all of the gases that make up our atmosphere, any free hydrogen gas simply floats away into space. Most of the hydrogen on Earth is locked in compounds. One of the most common compounds containing hydrogen is good old water, H2O. Most everyone has heard of water referred to as H2O, but do you know what that means? H 2O is the chemical formula for water it means that every molecule of water has two atoms of hydrogen and one atom of oxygen. Pretty cool huh, three pieces of gas turn into the most common liquid on Earth.
Water, without water, there would be no life on Earth, so water is pretty important to us. Over the next few weeks, we are going to learn some interesting facts about good old H 2O.
The water on the Earth’s surface is called the hydrosphere. The hydrosphere is usually divided into seven forms of water. These seven forms of water are the oceans, saltwater seas and lakes, rivers, freshwater lakes, the atmosphere, groundwater, and in glaciers and ice caps. Only a small part of the hydrosphere, or water is available for human use! The majority of the Earth’s water is contained in the oceans and seas. Altogether, the oceans cover between 70 and 75 percent of our planet.
Most people recognize five oceans: Pacific, Atlantic, Indian, Arctic, and the Southern Ocean. These five oceans are all connected together into one giant ocean, sometimes referred to as the World Ocean. The Pacific Ocean is the largest and deepest ocean. The Atlantic Ocean is the second largest, then comes the Indian Ocean, next comes the Southern Ocean, and the smallest Ocean is the Arctic. The Southern Ocean is all of the water south of the 60 degree S. latitude.
Oceanographers are scientists who study the oceans. All of the world’s oceans and seas contain saltwater and cannot be consumed by humans or animals. The oceans contain about 97% of all the Earth’s water. Drinking saltwater will make you very ill and can cause you to die. Ocean water has a salinity of 3.5%. When oceanographers refer to the salinity of the ocean, they are referring to the amount of salt and minerals dissolved in ocean water . So, salinity refers to how much salt is in ocean water. Gases, such as oxygen and carbon dioxide are also dissolved in the ocean and can move back and forth between the water and the air. The greatest amount of saltwater is found in the world ocean, but saltwater is also found in seas and salt lakes. Think about that, 97% of all the water on Earth cannot be easily used by mankind.
Ocean water is about 3.5% salt. That means that if the oceans dried up completely, enough salt would be left behind to build a 180-mile-tall, one- mile-thick wall around the equator! And more than 90 percent of that salt would be sodium chloride, NaCl, or ordinary table salt. The oceans sure contain a lot of salt.
This second graph gives you a better breakdown of the freshwater. You have to add the deep and shallow groundwater to get the total groundwater. Remember, different information sources may give you somewhat different facts. Since we can't actually measure the amount of water in the ground, we can say about 1/3 of the freshwater is useable.
Only 3% of the Earth’s water is fresh water. About 2/3 of that 3% or about 69% of the world’s fresh water is frozen in glaciers and ice caps at the North and South Poles. The Arctic Ocean surrounds the North Pole and a huge area of it stays frozen all year. Greenland, near the North Pole and Antarctica are almost completely covered in ice all year round. Many parts of the world also have glaciers. Glaciers are like huge rivers of ice that are slowly moving downhill or down the side of a mountain.
About 31% of the world’s freshwater or 1% of all the water on Earth, is useable by mankind. That sure doesn’t sound like a lot of water for us to use. So where can we find this little bit of freshwater that we get to use?
Most of the freshwater useable by mankind is found underground in groundwater. Most of the world’s useable freshwater is in groundwater. Less than 1 % of all useable freshwater on Earth is found in the lakes, rivers, swamps, and in the atmosphere.
This is an important concept, only about one percent of all the water on Earth is useable by mankind. That one percent is divided into groundwater, rivers, lakes, and the atmosphere. As we already said, most of the useable water is found in groundwater. Groundwater is water stored underground in huge areas of permeable rock and sand called aquifers. These aquifers can store water for thousands of years. Permeable rock has spaces or pores in it that can hold water. Layers of soil above an aquifer filter out pollution. Rural communities and families usually get their water from wells drilled down into the aquifers. Larger towns and cities may also use wells drilled into the aquifer, but cities also get some of their water from rivers and special lakes called reservoirs.
So, look at the picture above. If the pumping well takes water out of the aquifer faster than the precipitation and infiltration can refill it, what will happen to the water table and the stream? Eventually, what will happen to the pumping ell?
In some parts of the world where freshwater is very scarce, some countries use a process called desalination. Desalination is the process of removing salt from ocean water, making it drinkable. Desalination can be very expensive. Another problem is what to do with the salts and other materials removed from the ocean water. Think about it, if ocean water has a salinity of 3.5%, that means for every 1000 gallons of ocean water, you have nearly 35 pounds of salt to dispose of.