Water Science for Kids: Saltwater Desalinization Experiment

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Have you ever wondered why freshwater fish can’t live in the ocean and how saltwater fish survive in saltwater? So did we! In this Saltwater Desalinization Experiment, we investigated how saltwater fish survive in the ocean.

To illustrate how saltwater fish filter salt from their bodies, we conducted our own water science experiment for kids and made our own water distiller.

You’ll also want to check out the ultimate list of summer STEM activities and the ultimate list of summer science experiments. 

Related: STEM Activities for Kids

How Saltwater Fish Live in the Ocean

One day recently, the kids and I had a discussion about what allows saltwater fish the ability to survive in the ocean and whether freshwater fish could survive there.

Monkey thought that perhaps saltwater fish drank the saltwater and needed it to survive. This sparked an investigation of how saltwater fish survive in the ocean.

We read this lesson about how fish can stay alive in saltwater, and found that fish all fish filter the salt out of the water surrounding them. Most fish remove the excess salt through their kidneys, just like humans (but much more efficiently), but sharks have a chemical called urea that helps prevent salt overload in a shark’s body.

The shark has a special gland that removes salt through the digestive system.

Monkey wanted to know if it was possible for humans to remove salt from water, which sparked a discussion and investigation of how to remove salt from water. We learned that a process called “desalinization” is how salt is removed from water.

The simplest way to remove salt from water is to evaporate the water and collect it in a new container through water distillation, which leaves heavier salt particles behind.

Water Science for Kids: Desalinization Activity

You can filter your own freshwater with this simple water science for kids desalinization activity.

This post contains affiliate links for your convenience. 

Supplies

• Large glass container with a wide mouth (we used this one) (affiliate)
• Small glass container that is shorter than the walls of your first container (we used a small storage container) (affiliate)
• Kitchen plastic wrap (affiliate)
• Rock or other heavy object (but not heavy enough to break through the plastic film)
• Salt (affiliate)

Make saltwater by adding salt to two cups of water on the stove. To make the salt dissolve faster, we boiled our water. Mix the salt until it was completely dissolved into the water.

Next, fill your large bowl with the saltwater. Place the smaller container in the center of the bowl. Make sure you don’t splash any saltwater into the center bowl or your water will not taste fresh.

The center container should also sit on the bottom of the container and not move around. We had to pour out some of our saltwater until the water level was low enough to stabilize the center container.

Cover the top of the large bowl with plastic wrap. Place your rock on top of the plastic in the center of the small container. This will encourage the water that evaporates to drip into the center container.

Place the bowl in direct sunlight for several hours. Outside is best. We left our bowl in direct indoor sunlight for about five hours and were only able to collect about two tablespoons of water during that time.

When you can’t wait any more, remove your plastic wrap and test out your water. It should taste fresh!

In fact, our water tasted much better than our filtered water usually does. The process we used to desalinate the water is also how water distillation works, which is an effective water purifier. 

Monkey was not convinced that this water science for kids activity would produce freshwater until she drank the desalinized water we made. She was surprised at how effective it was!

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