Water for Schools
Menu

Lesson plan Grade 4 Science

Why the Munstock Wells Ran Low: Comparing Three Fixes

A grade 4 science lesson in which students use a fictional town's daily well budget to compare three ways of closing a summer groundwater shortfall.

Objectives

  1. Students will explain how rain soaking into the ground refills a shallow well field.
  2. Students will calculate a daily water shortfall and the effect of each proposed fix in gallons.
  3. Students will compare three solutions against stated criteria and defend one choice with numbers.

Vocabulary

Groundwater
Groundwater is water that has soaked into the ground and fills the spaces between soil particles and cracks in rock underground. It is a large underground source of fresh water that wells and springs draw from.
Recharge
Recharge is water soaking down through the ground to refill an aquifer, the way rain refills an underground sponge. Aquifers stay healthy only if recharge keeps up with pumping.

Also: well field, shortfall, reuse

Teacher overview

The fictional town of Munstock draws its drinking water from a field of shallow wells, and rain soaking through sand and gravel is the only thing that refills them. During one dry August the town pumped more each day than the ground put back, and the water level in the wells dropped week after week. This lesson gives students the daily numbers, has them find the gap between what goes out and what comes in, and then asks them to compare three ways of closing that gap. The misconception this lesson targets is that groundwater sits in an underground lake or river with a fixed floor. Students often assume a well simply runs dry all at once, when the water level actually falls gradually as long as pumping outpaces recharge, and rises again when the balance flips.

Procedure

Gravel jar demonstration (10 min): Fill a clear jar with gravel and pour water in slowly while students watch the water level climb through the spaces between the stones. Insert a clear straw as the well and draw water out with a pipette or turkey baster, never by mouth, while a partner pours more water in at the top. Ask students to describe, in their own words, what has to be true for the level in the jar to stay the same.

Building the budget chart (10 min): On chart paper, write two headings: water leaving the wells each day, and water soaking in each day. Fill in the Munstock numbers, which are 3,600 gallons pumped out and 1,500 gallons soaking in during that dry August. Have the class name the difference before you write it. Label the difference clearly as the daily shortfall. Tell students the Munstock numbers are kept small so the arithmetic stays manageable. One household alone uses about 300 gallons a day, so a real town with a park, a pool, and ball fields pumps tens of thousands of gallons a day or more.

Introducing the three fixes (10 min): Present each proposed solution on its own chart strip. Option A shortens the sprinkler run at the town park and saves 400 gallons a day. Option B sends rinse water from the pool filter to the ball fields instead of using well water, and saves 300 gallons a day. Option C builds a storage tank that is filled in winter and holds 8,400 gallons. Write the criteria beside them: the fix must cut the daily shortfall, must work during August, and must fit on land the town already owns.

Handout, items 1 to 6 (15 min): Students work items 1 through 6 in pairs. Circulate and check that students subtract the savings from the shortfall rather than from the pumping total. After ten minutes, run a quick check for understanding by asking every pair to hold up a whiteboard with their answer to item 5, and reteach at the board if more than four pairs disagree.

Ranking the fixes (5 min): Ask three pairs to rank the options from most to least helpful and to say which criterion decided the ranking. Point out that Option C stores water rather than saving it, so it helps only until the tank empties.

Exit ticket, item 7 (5 min): Students answer item 7 alone on an index card and hand it in. Any card that does not show a division or a repeated-addition step needs follow-up the next day.

Why the Munstock Wells Ran Low: Comparing Three Fixes — Grade 4 Science
Name: ____________________________ Date: ______________

Student Handout

In the town of Munstock the wells give up 3,600 gallons of water every day in August. Rain soaking into the ground puts back only 1,500 gallons a day that month. Use those numbers for the items below.

  1. How many more gallons leave the wells each day than soak back in?

  2. That daily shortfall lasts 5 days in a row. How many gallons is the shortfall over those 5 days?

  3. Option A saves 400 gallons a day. Start from a shortfall of 2,100 gallons a day. What is the new daily shortfall with Option A?

  4. Option B saves 300 gallons a day. Start again from a shortfall of 2,100 gallons a day. What is the new daily shortfall with Option B?

  5. Suppose the town uses Option A and Option B together, saving 400 gallons and 300 gallons a day. What is the daily shortfall then?

  6. The Option C tank holds 8,400 gallons. The town plans to spread that water evenly across 6 days. How many gallons would come out of the tank each day?

  7. With Options A and B in place, the shortfall is 1,400 gallons a day. The Option C tank holds 8,400 gallons. For how many days can the tank cover that shortfall?

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: 2,100 gallons.
    Subtract what soaks in from what is pumped out: 3,600 - 1,500 = 2,100 gallons a day.

  2. Answer: 10,500 gallons.
    Five days at 2,100 gallons a day gives 5 x 2,100 = 10,500 gallons.

  3. Answer: 1,700 gallons.
    Take the savings off the shortfall: 2,100 - 400 = 1,700 gallons a day.

  4. Answer: 1,800 gallons.
    Take the savings off the shortfall: 2,100 - 300 = 1,800 gallons a day.

  5. Answer: 1,400 gallons.
    The two fixes save 400 + 300 = 700 gallons a day, and 2,100 - 700 = 1,400 gallons a day.

  6. Answer: 1,400 gallons.
    Share the tank evenly: 8,400 divided by 6 equals 1,400 gallons a day.

  7. Answer: 6 days.
    Item 6 shows that 1,400 gallons a day for 6 days uses 8,400 gallons, which is the whole tank. Accept repeated addition of 1,400 six times as the same reasoning.

Differentiation

Support

Give these students a printed place-value chart for numbers through the thousands and let them work items 1 through 5 with base-ten blocks in hundreds. Preload the handout with the subtraction frames written out, such as 2,100 - 400 = ___, so the arithmetic is the only new work.

Extension

Ask students to write a fourth option of their own that saves at least 500 gallons a day, show the subtraction that proves it, and explain which of the town's three criteria their option meets and which one it might fail. Students can also work out how many days the Option C tank would last on its own with no other fix in place.

ELL supports

Pre-teach recharge, shortfall, and reuse with the gravel jar still on the table, pointing to the pouring and the drawing out as you say each word. Provide a two-column word bank of "water in" and "water out" phrases, and give sentence frames for the ranking discussion: "Option ___ helps most because it saves ___ gallons each day."

Extensions

Have students track a classroom version of the budget for one week, pouring a measured amount into the gravel jar each morning and removing a measured amount each afternoon, then graphing the level they observe. Pairs can also write a short letter to a fictional Munstock town council recommending one option and citing two numbers from their handout.