11.35 Desalination Lesson

Since the Earth is nicknamed the Blue Planet, you would think we have enough water to last us forever. However, almost all of the water on Earth is undrinkable saltwater. This lesson focuses on the process of turning that seawater into fresh, usable water.

Salt vs. Fresh Water

A cool glass of water can be very refreshing. Even though it may seem like there is an endless supply of water coming out of your faucet, it’s important to remember that only 2.5% of the water in the world is fresh water! Many people on Earth struggle to get a reliable supply of water, even if they live right next to an ocean. So if there is such a huge amount of ocean water on Earth, why can’t we just drink it? Well, if you took a gulp of salt water, you would probably get sick because of the bad taste. Besides that, you would get even thirstier because your body cannot handle that much salt.

What if we could turn the salt water into fresh water? You may be surprised to hear, but many places are already doing it with a process called desalination. This process involves separating and removing high amounts of salt from fresh water. There are places around the globe that perform this job, and they are called desalination plants. This newer technology just might be the future for our drinking water!

1. Main points:

The text emphasizes that only a small fraction of the world’s water is freshwater and discusses the challenges of using saltwater. It introduces desalination as a solution, explaining that this process removes salt from ocean water to make it drinkable, and highlights the potential of desalination plants in addressing global water needs.

2. Questions:

• Content Analysis: Why is ocean water not suitable for drinking as explained in the text?
• Contextual Analysis: What is the process of desalination and its purpose, according to the text?
• Thematic Analysis: How does the text suggest desalination plants might impact the future of our drinking water?

3. Further Discussion:

• How do you think desalination could change the way we use water in areas that don’t have much freshwater?

4. Answers:

• Content Analysis: The text explains that drinking salt water can make you sick and even thirstier because the body cannot handle much salt.
• Contextual Analysis: Desalination is described as a process that involves separating and removing high amounts of salt from fresh water, used to make ocean water drinkable.
• Thematic Analysis: The text suggests that desalination plants, with their ability to turn salt water into fresh water, might be the future for our drinking water.

How Desalination Works

There are a few ways that engineers can separate salt from water. One way is called distillation. Distillation is the process of heating up water so forcefully that it changes into a gas, and it leaves any little solid particles behind, including salt. Once the water cools, it turns back into a liquid, but now it is pure and fresh. When you heat up a pot of water on the stove, it takes about 10 minutes to boil. Can you imagine how much heat is needed to heat up, say, one million gallons of salt water?

Another way to desalinate water is called reverse osmosis. In reverse osmosis, salt water is forcefully pushed through a wall-like barrier that has many tiny holes in it. These holes allow the water to pass through, but they do not allow the tiny salt particles in the water to pass through. It acts like a very powerful filter, separating the salt and water.

1. Main points:

The text outlines two methods for desalinating water: distillation, which involves heating water to leave behind salt and other particles, and reverse osmosis, where water is pushed through a barrier with tiny holes that filter out salt particles, resulting in fresh water.

2. Questions:

• Content Analysis: How does the process of distillation work to remove salt from water, as described in the text?
• Contextual Analysis: What is the principle behind reverse osmosis in desalinating water, according to the text?
• Thematic Analysis: Why are these methods important for turning salt water into drinkable water?

3. Further Discussion:

• Which method do you think might be more effective for desalinating large amounts of water and why?

4. Answers:

• Content Analysis: Distillation works by heating water so forcefully that it changes into a gas, leaving solid particles like salt behind, and then cooling to form pure, fresh liquid water.
• Contextual Analysis: In reverse osmosis, salt water is pushed through a barrier with tiny holes, allowing water but not salt particles to pass through, acting as a powerful filter.
• Thematic Analysis: These methods are important as they provide ways to turn undrinkable salt water into fresh water, addressing global water scarcity issues.

The Future

If we keep using fresh water at the rate we are now, we’ll definitely need to depend on desalination in the future. Desalination is in the beginning stages; only about 2% of Earth’s usable water comes from desalination plants. As the years go by, the Earth’s population will only get bigger, so we’ll need even more fresh water, no matter the cost!

There are also some negative things that happen as a result of desalinating ocean water. For example, after the water is made fresh, there is a ton of really salty water left over. Many desalination plants dump this salty water back into the ocean, which causes all sorts of problems for sea creatures. Also, since desalination plants need to create so much heat, they are still burning about as much as power plants do, which is not good for the air around us. So we humans need to be responsible!

1. Main points:

The text discusses the increasing reliance on desalination due to high freshwater usage, noting that desalination currently provides a small fraction of Earth’s usable water. It also highlights the environmental impacts of desalination, including harm to sea creatures from the disposal of leftover salty water and significant energy consumption, emphasizing the need for responsible human actions.

2. Questions:

• Content Analysis: What percentage of Earth’s usable water is currently provided by desalination plants, according to the text?
• Socio-cultural Analysis: Why might the growing Earth’s population lead to an increased dependence on desalination, as mentioned in the text?
• Ideological Analysis: What are the negative environmental impacts of desalination highlighted in the text?

3. Further Discussion:

• How can we balance the need for more fresh water with the responsibility to protect the environment?

4. Answers:

• Content Analysis: The text states that only about 2% of Earth’s usable water comes from desalination plants.
• Socio-cultural Analysis: The growing Earth’s population will increase the need for fresh water, leading to a dependence on desalination because the current rate of freshwater usage is unsustainable.
• Ideological Analysis: The negative environmental impacts mentioned include problems for sea creatures due to the disposal of salty water and the high energy consumption of desalination plants, similar to power plants.

Lesson Summary

The Earth is mostly covered in salt water, but we cannot drink it unless it goes through desalination, which is the process of removing salt from water. There are a couple of ways desalination works, including distillation (boiling water to separate it from salt particles) and reverse osmosis (which is when saltwater is pushed through a powerful filter, separating the salt from the water). Along with the benefits, there are downsides to desalination, and we need to be responsible if we plan to use desalination in the future.