Lesson plan Grade 9 Science

Ferncliff's Lead Pipes: The Chemistry of Corrosion Control

A grade 9 lesson on how corrosion control chemistry keeps lead out of drinking water, using the Flint example and a fictional town's decision to evaluate the solution.

Grade: Grade 9
Subject: Science
Material: Lesson plan
Time: 45 min
Prep: No prep
Materials: Two images or written descriptions of pipe interiors, one coated with mineral scale and one bare, Index cards

Standards

HS-ESS3-4 NGSS

Evaluate or refine a technological solution that reduces impacts of human activities on natural systems.

How this material aligns: Students evaluate corrosion control treatment as a technological solution that reduces the impact of lead pipes on drinking water, and consider how the lower 2027 action level would refine it.

All materials for HS-ESS3-4 →

HS-ESS2-5 NGSS

Plan and conduct an investigation of the properties of water and its effects on Earth materials and surface processes.

How this material aligns: The lesson draws on a property of water, its action as a solvent, to explain how corrosive water dissolves lead from bare pipe walls and how a stable mineral scale forms a barrier that stops it, tying the chemistry to the scale's structure and function.

All materials for HS-ESS2-5 →

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This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-07-23.

Objectives

Students will explain how corrosion control treatment forms a protective layer that keeps lead from dissolving into drinking water.
Students will evaluate why removing corrosion control increased lead in Flint's tap water and how a lower action level tightens protection.

Vocabulary

Corrosion control: Treatment that keeps water from slowly eating away at the inside of pipes. It helps stop metals like lead from getting into drinking water.
Action level: A trigger number in lead and copper testing. If too many homes test above this level, the utility must take steps like improving treatment and telling the public.
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.
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: solvent

Teacher overview

Many older cities still carry drinking water through lead pipes, yet lead levels at the tap usually stay low because treatment plants add corrosion control chemistry that coats the inside of those pipes with a protective mineral layer. This lesson explains the chemistry behind that protection, uses the Flint water crisis as the example of what happens when corrosion control is removed, and asks students to evaluate the treatment as an engineered solution. A common misconception is that lead in tap water comes from the treatment plant itself; in fact it usually comes from the pipes between the main and the home, which is why the chemistry that protects those pipe walls matters so much.

Procedure

Hook (5 min): Show students two labeled images or descriptions: an old lead pipe with a dull mineral coating inside, and a bright, bare lead pipe. Ask which one they would rather have carrying their drinking water, and why. Record reasoning without confirming answers.

Direct instruction (15 min): Explain that water is a powerful solvent, able to dissolve small amounts of many materials, including lead from bare pipe walls. Corrosion control works by adjusting the water's chemistry, usually by controlling pH and adding a small amount of orthophosphate, so that a thin, stable scale forms on the inside of the pipe. That scale acts as a barrier between the water and the lead. Introduce the federal action level for lead, currently 15 ppb, and note that it is set to drop to 10 ppb in 2027 under updated rules, which also require replacing nearly all lead service lines within a decade.

Guided analysis (10 min): Walk through the Flint sequence as an example: in 2014 the city switched to more corrosive river water without adding corrosion control, the protective scale broke down, and lead leached into the water. Ask students to identify, at each step, where the protective chemistry was lost.

Small-group task (10 min): Give groups a scenario. Ferncliff, a fictional town, has many lead service lines but water that currently tests below the action level thanks to corrosion control. The town council asks whether corrosion control alone is enough. Groups list the strengths and weaknesses of relying on corrosion control and propose one refinement, such as service-line replacement or added monitoring.

Closure / exit ticket (5 min): On an index card, students answer three short questions: (1) How does corrosion control keep lead from dissolving into the water that flows through lead pipes? (2) Why did lead levels rise in Flint's tap water after the city changed its water source? (3) The federal action level for lead is dropping from 15 ppb to 10 ppb in 2027, and utilities must replace lead service lines; how does each of those steps strengthen protection against lead at the tap? Collect the cards and confirm at least 80 percent correctly explain that the protective scale, not the removal of the lead itself, keeps lead levels in the water low.

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: It forms a protective scale. Corrosion control adjusts pH and adds orthophosphate so a thin mineral layer coats the inside of the pipe, keeping water from dissolving the lead beneath it.
Answer: The corrosion control was removed. Flint switched to more corrosive water without corrosion control, so the protective scale dissolved and lead leached into the water.
Answer: Accept any reasoned answer noting that a lower action level (from 15 ppb to 10 ppb) means utilities must act on lead at a smaller concentration, and that replacing lead service lines removes the source of lead entirely rather than only coating it.

Differentiation

Support

Provide a labeled cross-section diagram of a pipe showing water, protective scale, and lead wall, and let students point to where corrosion control acts before writing their answers. Offer a word bank with "solvent," "scale," and "action level" for the exit ticket.

Extension

Ask students to research what a lead service line inventory is and to explain why identifying which homes still have lead pipes is a necessary first step before the required replacements can happen, then rank replacement versus corrosion control as long-term solutions.

ELL supports

Pre-teach "corrosion" (slow eating away of metal) and "scale" (a thin mineral coating) with simple images. Provide sentence frames for the exit ticket: "Corrosion control lowers lead in the water by ___" and "Flint's lead problem started when ___."

Extensions

Have students find out whether their own water utility publishes information about corrosion control and lead service lines in its annual water quality report, and summarize in a short paragraph what the utility says it does to keep lead out of the tap water.