Lesson plan Grade 7 English Language Arts
Water Residence Time at Ingleford: Explanatory Writing
A grade 7 ELA lesson where students compare how long water sits in the air and in a deep aquifer, then write an explanatory paragraph organized by contrast.
Objectives
- Students will define residence time and use the term accurately in a written explanation.
- Students will organize an explanatory paragraph around a comparison, using transitions such as by contrast and while.
- Students will explain why water pumped from a deep aquifer is not the same water that fell as rain last week.
Vocabulary
- Residence time
- Residence time is how long a drop of water typically stays in one part of the water cycle before moving on. Water passes through the air quickly but can stay underground for a very long time.
- Aquifer
- An aquifer is an underground layer of rock, sand, or gravel that holds water in the tiny spaces between its grains. Wells reach down into aquifers to bring water up to the surface.
- 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.
- Water cycle
- The water cycle is the continuous movement of water between the oceans, the air, and the land. The same water evaporates, forms clouds, falls as rain or snow, and flows back to the ocean before the process repeats.
- Evaporation
- Evaporation happens when liquid water, often warmed by the sun, turns into an invisible gas called water vapor that rises into the air. It is how water leaves oceans, lakes, and puddles.
Also: contrast
Teacher overview
The fictional town of Ingleford collects rain in cisterns at its school and pumps the rest of its supply from a deep well, which gives students two parts of the same water cycle sitting side by side. The writing task asks them to explain residence time, meaning how long a molecule of water tends to stay in one place before it moves on. Water spends about nine days in the atmosphere on average, while water in deep groundwater can stay for centuries or longer. A misconception worth naming directly is the idea that an aquifer is an underground lake or river with a current, and that a well therefore draws up last week's rain. Aquifers are saturated sand, gravel, or rock, and deep water often moves only inches a day, which is why the two residence times differ so sharply.
Procedure
Hook (5 min): Ask students to write a one-sentence guess answering, "If you drink a glass of well water, how long ago do you think that water fell as rain?" Collect three guesses on sticky notes and post them without comment.
Build the concept (12 min): Define residence time in plain terms and give the two anchor figures from the handout. Sketch a simple cross section on the board showing rain, soil, an unsaturated layer, and a saturated layer with a well screen in it. Explain that water in the saturated layer fills spaces between grains rather than flowing down an open channel, so it moves slowly. Return to the sticky notes and let students revise their guesses aloud.
Model the paragraph (10 min): Display an explanatory paragraph frame with four moves: a topic sentence that names residence time, a sentence defining it, two sentences that contrast the two examples, and a closing sentence that says why the difference matters. Draft the topic sentence and the first contrast sentence aloud, underlining each comparison transition such as "by contrast," "while," or "on the other hand."
Guided writing (16 min): Students complete the three handout items, ending with the full explanatory paragraph. Circulate and prompt any student writing a list of facts to add a transition that shows how the two examples relate.
Revision pass (8 min): Students reread their paragraph and check two things: that the definition of residence time appears in their own words, and that at least two comparison transitions link the examples. They mark each transition with a box.
Exit ticket (4 min): Each student writes one sentence answering, "Why can two glasses of water in Ingleford have such different ages?" Collect and sort responses into those that mention how water moves through the ground and those that do not, which shows who still needs the cross section in front of them.
Student Handout
Background: Two supplies in Ingleford
Ingleford is a fictional town in a broad farming valley. It gets water from two places.
The first is rain. The school collects roof runoff in cisterns and uses it to water the garden beds. That water fell from clouds over the valley within the past few days. On average, a water molecule stays in the atmosphere about nine days before it falls as rain or snow. Nine days is a short stay, because air can hold only a small amount of water vapor, and that vapor soon condenses and falls.
The second supply is the town well, which reaches a deep aquifer under the valley floor. An aquifer is not an underground lake. It is a layer of sand, gravel, or rock whose spaces are filled with water. Water enters the aquifer slowly, in a process called recharge, and then creeps through those spaces. In deep groundwater, water can stay for centuries or even for thousands of years before anything pumps it out. The water Ingleford drinks from that well may have soaked into the ground long before the town existed.
Scientists use one term for both cases. Residence time is the average length of time water stays in one part of the water cycle before it moves to the next part. The atmosphere has a short residence time. A deep aquifer has a very long one. The same water cycle contains both.
Write
- In your own words, define residence time. Do not copy the sentence from the background.
- Give the residence time for water in the atmosphere and the residence time for water in deep groundwater, using the background.
- Write an explanatory paragraph that answers the question, "Why does water spend so much less time in the atmosphere, where Ingleford's cistern water comes from, than in the aquifer under the town well?" Include a topic sentence, a definition of residence time in your own words, at least two comparison transitions, and a closing sentence about why the difference matters to the town.
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Answer Key
- Answer: Accept any accurate restatement, such as the average length of time water stays in one part of the water cycle before moving on. Responses that only give an example without a definition are incomplete.
- Answer: About nine days in the atmosphere, and centuries to thousands of years in deep groundwater. Both figures appear in the background section.
- Answer: Accept a paragraph that names residence time in the topic sentence, defines it without copying, and contrasts the two supplies with transitions such as "by contrast," "while," or "on the other hand." Strong responses explain the cause of the difference, which is that air holds only a little water and releases it quickly, while water in an aquifer moves slowly through the spaces between grains of sand, gravel, or rock. A closing sentence should note a consequence for Ingleford, such as that deep groundwater refills slowly and cannot be replaced in a single wet season.
Differentiation
Support
Provide the cross-section sketch on the handout rather than on the board, and give a sentence frame for item 3 ("Water in the atmosphere, where the cistern water comes from, has a short residence time because ___. By contrast, water in the town well ___."). Allow these students to explain the contrast aloud to a partner before drafting.
Extension
Ask students to add a second paragraph explaining what residence time suggests about pollution. If a chemical reaches a deep aquifer, how long might it stay, and how does that compare with a chemical that reaches a fast-moving stream? The paragraph should keep the same comparison structure.
ELL supports
Pre-teach "residence," "aquifer," "recharge," and "contrast" using the cross-section sketch and a jar of gravel filled with water, which shows that water can sit between grains rather than in an open space. Provide a transition word bank on a desk card so students can concentrate on the science idea while the linking words are supplied.
Extensions
Students can look up whether their own community uses surface water, groundwater, or both, then write one paragraph predicting which supply has the longer residence time and what that means for how carefully the source must be protected. A short letter to the local water department asking how deep the town wells are turns the lesson into local research.