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Lesson plan Grade 3 Science

Wrenmoor's Cloudy Tap Water: A Grade 3 Treatment Steps Lesson

A 50-minute grade 3 lesson in which students order the steps that clean creek water and compare two treatment plans for a made-up town.

Objectives

  1. Students will name the order of the steps that clean water at a treatment plant.
  2. Students will compare two treatment plans against a stated goal and a stated limit.
  3. Students will add and subtract liters of water in one-step word problems.

Vocabulary

Key words: settle, filter, chlorine, cloudy, treatment plant, liter

Teacher overview

The town of Wrenmoor in this lesson is fictional, and so is the creek it draws from, yet the sequence its crew follows is the one used at real conventional plants: screen out the large debris, let the heavy dirt settle, send the water through sand, then disinfect. Students watch a settling demonstration and then compare a settle-only plan with a settle-then-filter plan against a stated goal and a stated time limit. The misconception this lesson is built to correct is the belief that water which looks clear is therefore safe to drink, which is why the disinfection step is presented as necessary even after the jar looks fine. Third graders also tend to say that the dirt disappeared rather than that it moved to the bottom, so the demonstration keeps the settled layer where everyone can see it.

Procedure

Hook (5 min): Show the class a jar of tap water beside a jar of water you stirred a spoonful of garden soil into. Ask which one the town of Wrenmoor should send to its houses, then ask what the crew would have to take out of the cloudy jar first. Record two or three student ideas on the board without correcting them yet.

Settling demonstration (12 min): Pour one liter of the cloudy water into a clear jar and set it where every student can see it. Start a timer and leave the jar alone. While it sits, name the four steps a plant uses in order: screen, settle, filter, disinfect. Return to the jar at the ten-minute mark and ask students to describe the layer at the bottom and the water above it. Point out that the dirt moved rather than vanished.

Direct instruction (8 min): Pour the top part of the settled water through clean sand held in a funnel lined with a coffee filter, and catch it in an empty jar. Show the class the water that comes through. State plainly that this water is clearer but still not ready to drink, because germs too small to see can remain, which is why the last step adds a small amount of chlorine. Write the four steps in order on the board and leave them there.

Handout work (15 min): Distribute the handout and read the setup aloud. Students work items 1 through 7 on their own, then check items 1 through 4 with a partner. Circulate and watch for students who subtract when the problem asks for a total.

Closure and formative check (10 min): Collect the handouts. Ask every student to hold up fingers for the number of steps a plant uses before water goes to houses. Four fingers from at least three quarters of the class is the threshold for moving on; if fewer, reteach the order using the board list before the next session. Close by asking two students to defend the plan they chose in item 5.

Wrenmoor's Cloudy Tap Water: A Grade 3 Treatment Steps Lesson — Grade 3 Science
Name: ____________________________ Date: ______________

Student Handout

The town of Wrenmoor is a made-up place. Its crew takes water from Cobbleside Creek. After a storm the creek water is cloudy. The crew must clean it before it goes to houses.

The crew has two plans. Plan 1 lets the mud settle for one hour. Plan 2 lets the mud settle for half an hour and then sends the water through sand. Both plans must make the water clear, and both plans must finish in one hour.

  1. The crew pours 8 liters of creek water into Tub A. The crew pours 5 liters into Tub B. How many liters is that in all?
  2. Tub A holds 8 liters. The crew takes 3 liters of clear water off the top. How many liters are left in Tub A?
  3. Tub B holds 5 liters. Tub C holds 9 liters. How many more liters are in Tub C than in Tub B?
  4. The crew fills 4 jugs with clean water. Each jug holds 2 liters. How many liters is that in all?
  5. Wrenmoor needs clear water in one hour. Which plan should the crew pick? Tell why.
  6. Name one thing the crew must keep the same when it tests both plans.
  7. Put these three steps in the right order: send the water through sand, let the mud settle, add a small amount of chlorine.

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: 13 liters. Add the two pours: 8 plus 5 is 13.
  2. Answer: 5 liters. Take the scooped water away: 8 minus 3 is 5.
  3. Answer: 4 liters. Compare the two tubs: 9 minus 5 is 4.
  4. Answer: 8 liters. Four jugs of 2 liters each is 4 times 2, which is 8.
  5. Answer: Plan 2. Accept any answer that chooses the settle-then-filter plan and gives a reason tied to the two stated conditions, such as the sand catching dirt that is still floating after half an hour so the water is clear inside the hour. A student who picks Plan 1 should be asked what happens to the dirt still floating at the end of the hour.
  6. Answer: Accept any real control from the setup, including the same creek water, the same amount of water in each tub, the same tub size, the same starting time, or the same person judging whether the water looks clear.
  7. Answer: Settle, then sand, then chlorine. The mud settles first, the sand catches what is left floating, and the chlorine goes in last so the water stays protected on its way to houses.

Differentiation

Support

Give these students a handout with items 1 through 4 already set up as equations with one blank each, and let them use counters or a number line. Provide a four-card strip with the treatment steps printed on it so item 7 becomes a sorting task rather than a writing task, and read the setup paragraph aloud a second time before they begin.

Extension

Ask students to design a third plan for the town of Wrenmoor that uses sand first and settling second, then predict in writing whether it would meet both stated conditions. Have them explain what would happen to the sand if the muddiest water reached it before any of the dirt had settled out, and what the crew would have to do about it.

ELL supports

Pre-teach "settle," "filter," and "cloudy" with the demonstration jar and a hand motion for dirt sinking. Post the four step words in order with a small drawing beside each. Provide the frames "I pick Plan ___ because ___" for item 5 and "The crew must keep ___ the same" for item 6, and allow item 7 to be answered by numbering the printed step cards.

Extensions

Set up a second settling jar at the start of the school day and leave it undisturbed until dismissal. Have students draw the jar in the morning and again in the afternoon, then write one sentence comparing the two drawings. Ask them what an operator at the fictional Wrenmoor plant would gain by giving the water more settling time, and what the operator would lose.