Classroom activity Grade 10 Science

Westhorne's Cross-Connection Hazard Hunt Stations

A 50-minute grade 10 station rotation where teams inspect six cross-connection sites, choose backflow assemblies, and calculate the pressures that drive backflow.

Grade: Grade 10
Subject: Science
Material: Classroom activity
Time: 50 min
Prep: Low prep
Materials: Six printed station cards, Printed student handout, Calculators, Timer

Standards

HS-ETS1-3 NGSS

Evaluate a solution to a complex real-world problem based on prioritized criteria and trade-offs that account for a range of constraints, including cost, safety, reliability, and aesthetics as well as possible social, cultural, and environmental impacts.

How this material aligns: Teams recommend one of four protective assemblies at Stations 1 through 3 by weighing the hazard class against how reliably each assembly holds and whether its failure would be visible, which item 8 asks them to justify.

All materials for HS-ETS1-3 →

HSN-Q.A.1 Common Core Math

Use units as a way to understand problems and to guide the solution of multi-step problems; choose and interpret units consistently in formulas; choose and interpret the scale and the origin in graphs and data displays.

How this material aligns: Items 5 and 6 ask students to carry units through conversions between feet of water column and pounds per square inch, choosing the correct factor for each direction.

All materials for HSN-Q.A.1 →

Download Word file

This material is in the public domain (CC0) and may be copied, edited, and shared freely, without attribution. Updated 2026-09-04.

Objectives

Students will match each cross-connection hazard to an appropriate backflow assembly.
Students will convert between pressure in pounds per square inch and feet of head.
Students will explain how a pressure drop can pull contaminated water into a water main.

Vocabulary

Cross-connection: A cross-connection is any place where drinking water pipes are linked to something dirty, like a garden hose left sitting in a bucket of soapy water. If the flow reverses, the dirty water can get sucked in.
Backflow: Backflow is water flowing backward through a pipe in the wrong direction, which can pull dirty water into the clean drinking water system. Special devices are installed on pipes to stop it.

Also: backsiphonage, air gap, reduced-pressure assembly, vacuum breaker

Teacher overview

A cross-connection is any point where drinking water can meet something else, and for most of the time the pressure in the main keeps the water moving in one direction only. When that pressure drops or a pump on the customer's side pushes back, the connection can run in reverse. In this station rotation, teams of three or four inspect six sites in the fictional town of Westhorne, decide how dangerous each connection is, choose a protective assembly, and work the pressure arithmetic that explains why the assembly is needed. The exercise mirrors the work of a cross-connection control inspector, who walks a route and writes findings of this kind.

Activity Directions

Before class, print the six station cards below and place them around the room with space for a team to stand at each. Print one handout per student. Every site described here is invented for the fictional Westhorne water system.
Briefing (8 min): Define cross-connection, backflow, backsiphonage, and backpressure. Explain that backsiphonage happens when the main loses pressure and sucks water backward, while backpressure happens when a pump or tall column on the customer's side pushes harder than the main. Name the four protections students will choose among: an air gap, a hose bib vacuum breaker, a double check valve assembly, and a reduced-pressure principle assembly. State the rule of thumb that a health hazard requires an air gap or a reduced-pressure assembly, or a vacuum breaker where only backsiphonage can occur, while a non-health hazard may use a double check valve assembly.
Assign teams to starting stations, one team per card.
Rotation (30 min): Teams spend five minutes at each of the six stations and answer the handout items that name that station before the timer sounds. Call the rotation yourself so every team moves at once.
Station 1, Harbrook Warehouse: A fire sprinkler system holds city water in a standpipe with no antifreeze and no chemical additives. The water sits still for months.
Station 2, Kestrel Lane house: A garden hose runs from a hose bib into a swimming pool and is left lying under the surface.
Station 3, Westhorne Golf Course pump house: A fertilizer injector feeds liquid nutrient into the irrigation line, which is connected to the city main and stays pressurized.
Station 4, Westhorne Golf Course main line: The irrigation booster pump holds 118 psi on the customer side of a check valve while the city main holds 62 psi.
Station 5, Harbrook Warehouse roof: A storage tank stands 85 feet above the water main that serves it.
Station 6, Bellwood Veterinary Clinic: A hose bib fills a livestock trough. During a main break on the same block, the pressure at that hose bib fell to 4 psi.
Debrief (12 min): Bring the class together and ask two questions. First, which of the six sites would you inspect again next year, and why? Second, why does a health hazard under backpressure require an air gap or a reduced-pressure assembly rather than a check valve? Take answers from three teams before revealing the key.

Westhorne's Cross-Connection Hazard Hunt Stations — Grade 10 Science

Name: ____________________________ Date: ______________

Student Handout

Suppose you are inspecting cross-connections for the fictional Westhorne water utility. Every site and figure below is invented for this activity. Use 0.433 psi per foot of water and 2.31 feet of head per psi.

Station 1 is a warehouse fire sprinkler system filled with plain city water, with no antifreeze and no additives. Inspectors classify it as a non-health hazard. Name the backflow assembly the utility should require.
Station 2 is a garden hose left lying in a swimming pool. Treated pool water is a health hazard. Name the protection the homeowner should install at the hose bib.
Station 3 is a fertilizer injector on a golf course irrigation line that stays under constant pressure. Liquid fertilizer is a health hazard. Name the assembly the utility should require.
At Station 4 the irrigation booster pump holds 118 psi on the customer side of a check valve while the city main holds 62 psi. Calculate the pressure difference pushing irrigation water toward the main.
At Station 5 a rooftop storage tank stands 85 feet above the water main. Calculate the pressure that 85-foot column of water places on the main at the bottom of the supply line.
The Westhorne main normally holds 62 psi. Convert that pressure to feet of head.
At Station 6 the pressure at a hose bib fell to 4 psi during a main break. Most states require a minimum of 20 psi in the distribution system. Calculate how far below that minimum the pressure fell.
Explain why a single check valve is not accepted at a connection where a chemical could be pushed back into the main.

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: A double check valve assembly. The sprinkler water is stale but not a health hazard, so a double check valve assembly is the accepted protection for that class of connection.
Answer: A hose bib vacuum breaker. Treated pool water is a health hazard, and a vacuum breaker on the bib stops backsiphonage when the main loses pressure. Keeping the hose end above the rim of the pool would create an air gap and give the same protection.
Answer: A reduced-pressure principle assembly. A health hazard on a line that stays pressurized requires either an air gap or a reduced-pressure assembly, and an air gap is not practical on a pressurized irrigation line.
Answer: 56 psi. The difference is 118 - 62 = 56 psi pushing from the customer side toward the main.
Answer: 36.8 psi. Pressure = 85 feet x 0.433 psi per foot = 36.8 psi.
Answer: 143.2 feet. Head = 62 psi x 2.31 feet per psi = 143.2 feet of head.
Answer: 16 psi. The pressure fell to 4 psi, and 20 - 4 = 16 psi below the minimum.
Answer: A single check valve has one moving part and no way to show that it has failed. Grit, scale, or a worn seat can hold it open, and nothing outside the pipe would reveal the problem. A reduced-pressure assembly uses two independent checks with a relief valve between them that dumps water to the ground when either check leaks, so a failure becomes visible before contamination reaches the main.

Differentiation

Support

Give these students a reference card at every station listing the four protections with a one-line description and a picture of each. Pair them with a partner for the two conversion items and allow a calculator with the conversion factors already written at the top of the handout.

Extension

Ask teams to write a seventh station card for a site in their own school, name the hazard class, and justify the assembly they would require. Have them explain what an inspector would look for to confirm the assembly still works.

ELL supports

Pre-teach "cross-connection," "backflow," "hose bib," and "assembly" with labeled photographs or simple drawings before the rotation begins. Provide the sentence frame "This site is a ___ hazard, so the utility should require ___," and allow teams to discuss in their home languages at the stations.