Purification of Salt Water
5 Minutes
Purification of salt water for kids: learn how seawater is turned into drinking water through distillation and reverse osmosis. An English science lesson.
- Why we cannot drink seawater and what desalination means
- Using evaporation and condensation to distill salt water
- How reverse osmosis uses a semi-permeable membrane
What this lesson teaches
Desalination is the process of removing salt from seawater so it can be turned into fresh drinking water. Although water covers seventy percent of the Earth, nearly ninety-six percent of it is salty ocean water that is unsafe for humans and animals to drink.
Why seawater must be purified
Most living beings on Earth quench their thirst using fresh water found in rivers, lakes, and groundwater. The remaining thirty percent of our planet is land, which is where all people, trees, creepers, and animals live. Even though the Earth appears bright blue from space because of all the water, salty seawater is not safe for our bodies to consume. Desalination makes ocean water usable by taking out the salt through either distillation or reverse osmosis.
How distillation works
Distillation separates salt and water by using heat, evaporation, and condensation. Salt water is placed inside a flask and heated until the water turns into vapor and rises. All of the salt stays behind and settles at the bottom of the flask because salt does not turn into vapor. When the clean water vapor cools down, condensation turns it back into liquid water that contains no salt.
How reverse osmosis works
Reverse osmosis is the most common method used to turn seawater into good drinking water. A container is divided into two sections by a semi-permeable membrane, which is a filter with extremely tiny holes. These tiny openings stop salt, chemicals, and bacteria from passing through, allowing only water molecules to cross. When pressure is applied to the salt water side, pure water is forced through the membrane while the salt remains trapped, similar to squeezing lemon juice away from pulp and seeds.
The stages of reverse osmosis
- Pretreatment filters out large objects from the seawater, including discarded bottles and waste plants.
- Reverse osmosis uses pressure to separate and remove the salt through the semi-permeable membrane.
- Chemical treatment mixes substances into the purified water to destroy any germs that are invisible to the eye.
- Mineral addition puts back the healthy minerals needed by our bodies that were filtered out during the process.