Why Can’t We Just Drink the Ocean?

Many of our activities with Ms. Berryhill’s Earth Sciences class at McCurdy have related to water quality. Water is a critical issue in New Mexico. With decreasing snowpack and increasing water use, we’re headed for trouble. On two previous visits to McCurdy, students asked, “Why can’t we just take the salt out of sea water?”

“Well, it takes quite a bit of energy, and it’s expensive.” we said.

Why tell them this when you can show them?

This is exactly what we did with the students yesterday. First we discussed methods of purifying water. Some of these (like adding chemicals) just won’t work for taking the salt out of water. Most of the students quickly figured out that distillation would be a good method we could test in class.

We briefly discussed the process of desalination and compared the prices of desalinated water in different parts of the world, and then the students were free to create their own devices to distill salt water with the materials we brought. We had two main methods: one using a camp stove and one using the energy of the sun.

This iteration used plastic wrap to catch the condensed water. Unfortunately, the plastic wrap melted. The students replaced it with aluminum foil.
This group made an aluminum foil pipe to carry the distilled water down to a catchment.
This was a very creative system.
These students added ice to their pie pan to speed up condensation. When asked what they would change, they said they would put aluminum foil around the sides so that the steam didn’t escape.
There’s a coffee cup inside this kettle. This method made an interesting comparison to how clouds form (which we discussed last month).
One of the methods that used the sun to force evaporation. This was very effective.

After we finished building these devices, we compared them. Using a camp stove takes less time but uses fuel. The fuel for the solar version is the sun, but it takes more time. Either way, it takes quite a bit of energy to desalinate water!


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