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Reading passage Grade 5 Science

How Dernwood Point Makes Tap Water From the Sea

A grade 5 informational passage about a fictional coastal town whose wells turned salty, the membrane plant it built, and why it still asks families to save water.

Objectives

  1. Students will locate stated details in an informational passage about a coastal water plant.
  2. Students will quote a sentence accurately and explain its meaning in their own words.
  3. Students will explain why a town that can make fresh water still asks families to save it.

Vocabulary

Brine
The extra-salty water left over after desalination pulls fresh water out of seawater. Plants must dispose of it carefully so it does not harm sea life.
Desalination
Turning salty water, like ocean water, into fresh water people can use. It works, but it takes a lot of energy and leaves behind very salty water that must be handled carefully.

Also: membrane, well, seawater

Teacher overview

This original passage is set in the fictional coastal town of Dernwood Point, where the wells turned salty and the town built a plant that takes salt out of seawater. A student narrator reports what her aunt, who works at the plant, showed her on a Saturday visit. Teachers can assign it to introduce membranes and brine before any lab work, or to give students a reading-based reason for why conservation still matters in a town that can make its own fresh water. Many students assume that salty water can be made drinkable by boiling or by pouring it through a filter, and the passage addresses that directly by explaining that the salt is spread through the water in pieces far too small for a filter to catch.

How Dernwood Point Makes Tap Water From the Sea — Grade 5 Science
Name: ____________________________ Date: ______________

Passage

My aunt Nell works at the water plant in Dernwood Point. Our town sits right on the coast. I asked her once why our tap water used to taste like the sea. She told me the whole story on the drive to school.

Dernwood Point used to drink from wells. The wells reached down into sand and gravel under the town. Rain soaked in each winter and refilled them. That worked for a long time.

Then the town grew. More houses meant more pumping. The wells pulled water out faster than rain could put it back. Ocean water crept in to fill the empty space. Bit by bit, the well water turned salty. Boiling does not take the salt out of a pot of salty water. The water leaves as steam, and the salt stays behind. You cannot catch it in a coffee filter either. The salt is spread all through the water in pieces far too small to see.

So the town built a plant that takes the salt out of seawater. The long word for that work is desalination.

Aunt Nell walked me through the whole building one Saturday. First, seawater comes in through a metal screen. The screen catches seaweed, shells, and lumps of sand. Next the water passes through filters that trap smaller specks. Then comes the part my aunt calls the heart of the plant.

Strong pumps push the water hard against thin sheets called membranes. The openings in a membrane are far too small for salt to fit through. Water squeezes through, and salt stays behind. Clean water gathers on the far side and heads out to the town pipes.

The salt still has to go somewhere. What stays behind is water with much more salt in it than the sea has. Workers call that brine. At Dernwood Point the brine gets mixed with a large amount of plain seawater first. Then it flows out through a pipe on the seafloor. The mixing keeps any one spot from turning too salty for crabs and fish.

I asked my aunt whether the town's water worries were over now. She said they were not.

The pumps at the plant use a great deal of electricity. Making water this way costs far more than lifting it from a well. So Dernwood Point still asks families to fix drips and to water gardens early in the morning. Aunt Nell says that saving a gallon is always cheaper than making one.

Here is the part I keep thinking about. About 97 out of every 100 parts of Earth's water sits in the ocean. About 2 more parts are locked up as ice. That leaves less than 1 part in 100 as fresh water people can reach. Our town used up its share of that small part. Now we spend money and power to borrow from the big salty part instead.

Questions

  1. Why did the water in Dernwood Point's wells turn salty?
  2. What happens to the water and to the salt when the pumps push seawater against a membrane?
  3. What does the word brine mean in this passage?
  4. Why does the plant mix the brine with a large amount of plain seawater before sending it back out to sea?
  5. Find the sentence in the passage that tells what happens to the water and the salt at the membrane. Copy that sentence exactly. Then explain in your own words what it means.
  6. Aunt Nell says that saving a gallon is always cheaper than making one. Use details from the passage to explain what she means.
  7. The passage says that less than 1 part in 100 of Earth's water is fresh water people can reach. Explain how that idea helps you understand why Dernwood Point built its plant.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key
  1. Answer: The town pumped the wells faster than rain could refill them. The passage says more houses meant more pumping, and ocean water crept in to fill the empty space, so the well water slowly turned salty.
  2. Answer: The water goes through and the salt stays behind. The passage explains that the openings in a membrane are far too small for salt to fit through, so clean water gathers on the far side.
  3. Answer: Water that is much saltier than the sea. The passage says the brine is what stays behind after the fresh water is pushed through the membrane.
  4. Answer: To keep one spot in the sea from turning too salty. The passage says the mixing protects crabs and fish near the end of the seafloor pipe.
  5. Answer: "Water squeezes through, and salt stays behind." Students should copy it word for word, then explain that the membrane lets water pass but blocks the salt, which is how the plant separates the two.
  6. Answer: Making fresh water at the plant takes strong pumps and a great deal of electricity, which costs far more than lifting water from a well. A gallon that nobody wastes is a gallon the plant never has to make, so fixing a drip saves the town money and power.
  7. Answer: Almost all of Earth's water is salty ocean or frozen ice, and only a small part is fresh water people can reach. Dernwood Point used up its share of that small part when the wells turned salty, so the town had to turn to the ocean instead. Accept any answer that connects the small fresh share to the town's decision.

Differentiation

Support

Read the passage aloud once while these students follow along, pausing after every two or three paragraphs to summarize in a sentence. Give them a copy with the sentences that answer questions 1, 2, and 3 marked in the margin, so their work is explaining rather than searching.

Extension

Ask these students to write a short letter from Aunt Nell to the town council arguing either that the town should build a second plant or that it should spend the same money on fixing leaks. They must use at least three details from the passage and say plainly which choice they recommend.

ELL supports

Provide picture cards for well, screen, membrane, and brine, with a simple sketch on each showing what the water looks like at that step. Pre-teach squeeze, crept, and spread with gestures, and allow questions 3, 4, and 6 to be answered with a labeled drawing plus a short phrase.

Extensions

Have students find out whether their own community's water comes from wells, a river, or a reservoir, using a printed water quality report the teacher supplies, and write a paragraph comparing that source with what Dernwood Point had before and after the plant opened.