Earth is a watery planet. Wide blue oceans cover about 70 percent of its surface. This water represents about 97 percent of all the water on Earth. And it is salt water; too salty to be used by people for drinking, growing plants, or in industry.
Give Me Fresh Water
Humans drink a lot of water. It must be fresh water, not salty ocean water. People tend to live around freshwater sources such as lakes, rivers, and underground springs. Freshwater is needed to irrigate the plants people need for food. Much water is required by industry to build the products people have come to rely on. As this water is used it is replenished mostly by rain. Even so, every last drop on Earth eventually makes its way back into the ocean.
The salt water of the oceans creates most of the rain that falls to earth as fresh water. Through evaporation, water particles rise as vapor and leave the ocean salt behind. This moisture in the air accumulates as clouds and eventually falls back to earth as rain or snow. Green plants also add moisture to the air. A tree may give off 75 gallons of water a day. A corn field may give off 4,000 gallons of water per acre. These green sources are important.
Water Shortage and Desalinization
The human need for freshwater is constant. A shortage of fresh water is troubling. In desert regions, fresh water is always scarce. Other regions may have water shortage during times of drought. The verse “Water, water everywhere, Nor any drop to drink” celebrates the special plight of the mariner. On a ship in the middle of the ocean, a lack of fresh water is a tragedy. Surrounded by water, sailors can still die of thirst.
Seawater should never be drunk because of its high salt content. But since so much of the water on earth is salt water, surely some of it can be made into drinking water? Technology is being developed to desalinize sea water and turn salt water into fresh, drinkable water. There are several basic approaches.
- Solar Distillation Sunlight evaporates the seawater, freshwater vapor rises, salts and minerals are left behind. This fresh water is then collected.
- Reverse Osmosis Seawater is passed through fine osmotic membranes. Pressure through the membranes separates salts from the fresh water. If you have a water softener on your house, you can check how it works and softens water.
- Electrolysis Salt water is separated into oxygen and hydrogen parts and then recombined into pure water.
Man-made systems for desalinization are working now, but are not yet truly practical. The cost is high, it is not energy efficient, and there is an environmental impact to be considered.
How about a nice refreshing glass of seawater?
Desalinization by distillation is not modern science. Many early civilizations used this water treatment solution. If you can boil water, you can do it yourself.
- Get a large pot and place a glass cup in the center of the pot to collect the water.
- Pour the salt water or water to be treated into the pot around the collection cup. Be careful not to splash into the cup.
- Place the pot lid upside down over the pot so that the handle is hanging over the cup.
- Bring the water to a slow boil.
As the water boils, water vapor rises as steam. This freshwater vapor condenses on the pot lid and rolls as droplets into the collection cup. Let the water cool down and the result is drinkable fresh water.