Lesson plan Grade 6 Science
The Coating Inside Drenmoor's Lead Pipes: A Pipe-Wall Model
A grade 6 science lesson in which students model the protective layer inside a lead service line and use a fictional tap record to explain why lead results jumped.
Objectives
- Students will build a labeled model of a lead pipe wall with its protective coating.
- Students will use a tap sampling record to explain why lead results rose and then fell.
- Students will propose where and when a utility should sample to detect a lead problem.
Vocabulary
- Orthophosphate
- A chemical that utilities add to water in very small amounts. It coats the inside of pipes so lead cannot easily get into the water.
- pH
- pH is a number that tells whether water is acidic, like lemon juice, or basic, like baking soda mixed in water. Pure water sits in the middle of the scale at a pH of 7.
- Service line
- A service line is the small pipe that connects the water main under the street to the plumbing inside one home or building. It is the last leg of the trip water makes to your tap.
Also: corrosion, scale, parts per billion
Teacher overview
A lead service line does not release lead at a steady rate. Whether lead reaches the tap depends on the water traveling through the pipe, because treated water leaves behind a thin mineral coating that separates the metal from the water. In this lesson students build a labeled cross-section model of that pipe wall, then read a ten-year tap sampling record from a fictional street and use the model to explain why the numbers rose sharply one year and came down slowly afterward. The misconception to name during the hook is the assumption that a jump in lead results means the pipes themselves changed, got older, or cracked. The pipes in this scenario are the same pipes throughout. What changed was the chemistry of the water sent through them, which dissolved part of the coating that had been holding the lead in place. Students who look for a change in the pipe will not be able to explain why the numbers came back down without any pipe being replaced.
Procedure
Hook (5 min). Show the class two numbers from the fictional Drenmoor record without any explanation: the highest tap result in Year 6 and the highest result in Year 8, which is more than four times as large. Ask what could have happened on that street. Record every idea on the board. Most classes propose that pipes broke, aged, or were disturbed; leave those ideas posted.
Build the model (15 min). Give each pair the pipe cross-section sheet. It shows a circle cut through a service line, with the pipe metal as a thick ring and the water in the middle. Pairs add a thin inner layer of clay or a paper strip between the metal and the water and label three parts: the lead metal, the mineral coating, and the water. They then write one sentence under the drawing explaining what the coating does. Teach the mechanism directly at this point. Water that is slightly acidic, or water with no added phosphate, dissolves the coating. When a utility adds orthophosphate and raises the pH a little, minerals build a low-solubility layer on the inside of the pipe, and the water no longer touches bare metal.
Read the record (12 min). Distribute the Student Handout. Pairs study Table 1 and mark, on their model drawing, which years the coating was thick and which years it was thin. Ask pairs to say aloud what happened in the year the source changed before they write anything.
Use the model (10 min). Pairs answer questions 1 through 6. Circulate and press on question 4, where students must explain the slow recovery rather than an instant one. The coating rebuilds over months as treated water flows past, so the numbers fall gradually.
Formative check (8 min). Collect an exit ticket: each student writes one sentence answering "What changed in the year the lead results jumped?" Sort the tickets as students leave into those that name a change in water chemistry, those that name a change in the pipes, and those that name neither. If more than a third name a change in the pipes, reteach with the Support demonstration before the next lesson.
Close (5 min). Return to the ideas posted during the hook and ask which ones the record rules out. Note that this pattern is not only a classroom scenario: in 2014 Flint, Michigan switched its water source to the Flint River without corrosion-control treatment, and lead leached from the pipes.
Student Handout
Drenmoor is a fictional town and Wrenshaw Street is a fictional street. The record below was written for this lesson. The homes on Wrenshaw Street were built in the 1930s, and each is served by a lead service line running from the water main to the house. None of those lines was replaced during the years shown.
Table 1. Highest lead result at a Wrenshaw Street tap, by year
| Year | What the utility did | Highest tap result |
|---|---|---|
| Year 1 | No corrosion control treatment | 21 ppb |
| Year 3 | Began adding orthophosphate and raised pH slightly | 9 ppb |
| Year 6 | Same treatment, no changes | 6 ppb |
| Year 8 | Switched to a new river source; treatment paused four months | 26 ppb |
| Year 9 | Restored orthophosphate and pH adjustment | 11 ppb |
| Year 10 | Same treatment, no changes | 7 ppb |
For comparison, the federal lead action level is 15 ppb, and it drops to 10 ppb in 2027 under the Lead and Copper Rule Improvements.
Answer each question in complete sentences.
- In which year was the highest tap result recorded, and what had the utility done that year?
- Using your model, explain what the orthophosphate and the pH adjustment do inside the pipe.
- The lead service lines were never replaced during these ten years. Explain how the tap results could change so much while the pipes stayed the same.
- Between Year 8 and Year 10 the results fell, but not all at once. Use your model to explain why the recovery took two years instead of happening the moment treatment restarted.
- Compare the Year 9 result with the action level that takes effect in 2027. What does that comparison tell the utility?
- Design a sampling plan for Wrenshaw Street for the next year. Name where you would sample, how often, and what result would tell you the coating was thinning again.
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: Year 8, when the utility switched to a new river source and paused corrosion control treatment for four months. The tap result that year was 26 ppb.
- Answer: They build and maintain a thin mineral coating on the inside of the pipe. The phosphate forms a layer that does not dissolve easily, and raising the pH makes the water less corrosive, so the water flows against that layer instead of against bare lead.
- Answer: The lead reaching the tap depends on the water, not only on the pipe. When the water dissolved the coating, water touched bare lead and carried lead away. When the coating was rebuilt, the same pipes released far less lead.
- Answer: The coating has to rebuild. Minerals deposit slowly as treated water passes through the pipe day after day, so the layer thickens over months. Until it is fully rebuilt, some bare metal is still in contact with the water, which is why Year 9 is better than Year 8 but still higher than Year 6.
- Answer: The Year 9 result of 11 ppb is under the current action level of 15 ppb but above the 10 ppb level that takes effect in 2027. Accept answers stating that the utility would need to lower lead further, because results above the action level call for required steps such as public notice. The action level is a trigger for action, not a safe amount of lead.
- Answer: Accept any plan that names a location, a frequency, and a trigger. A strong plan samples first-draw water at taps served by lead lines, repeats at least quarterly, adds sampling after any change in source or treatment, and treats a rise across several homes at once as a sign the coating is thinning.
Differentiation
Support
Run a two-minute demonstration first: set a clean nail and a nail coated in petroleum jelly in two cups of vinegar and check them at the end of the period. Give these pairs a cross-section sheet with the three labels already printed and a word bank of "metal," "coating," and "water." Reduce the handout to questions 1 through 4 and provide the sentence frame "The results changed because the ___ changed, not because the ___ changed."
Extension
Ask a pair to draw what the pipe wall looked like in Year 1, Year 6, Year 8, and Year 10, four drawings in a row with a caption under each, then write a short paragraph explaining what a utility should check before switching to a new source. A second option is to research what their own state requires a utility to tell customers when a tap sample is over the action level.
ELL supports
Pre-teach "coating," "dissolve," "corrosion," "service line," and "sample" with the labeled cross section and a physical object students can hold, such as a plastic pipe fitting or a rolled paper tube with a paper lining. Provide a bilingual glossary card. Let students point to parts of the model while explaining, and accept labeled drawings for questions 2 and 4. Give the table with the Year 8 row highlighted so the key event is easy to locate.
Extensions
Have students find out whether their own water utility publishes a lead service line inventory, and report what the inventory says about the street their school sits on. A second option is to write the short notice the fictional Drenmoor utility would mail to Wrenshaw Street residents in Year 8, in plain language, explaining what changed, what the utility is doing, and what residents can do while the coating rebuilds.