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Worksheet Grade 7 Health & Consumer Science

Quorley's Backyard Cross-Connections: Air Gaps and Hose Risks

Students apply a two-times air gap rule to three faucets, judge four household hose setups for backflow risk, and find the percent of inspected homes with a risk.

Objectives

  1. Students will calculate a minimum air gap from a faucet opening width using a proportional rule.
  2. Students will identify cross-connection risks in household situations and name the correct fix for each.
  3. Students will explain how a pressure drop in the street main can pull water backward into a home.

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: air gap, vacuum breaker, hose bibb

Teacher overview

Ordinary household fixtures are kept safe by water pressure and by physical separation rather than by valves, so when pressure in the street main drops during a break or a hydrant flush, water in a hose or a filled sink can travel backward into the pipes that supply drinking water. This worksheet uses the fictional town of Quorley to teach the two protections a family controls, which are an air gap and a hose bibb vacuum breaker. The misconception worth naming first is that water can only travel one direction through a pipe, which holds only as long as the pressure behind it stays higher than the pressure ahead of it.

Quorley's Backyard Cross-Connections: Air Gaps and Hose Risks — Grade 7 Health & Consumer Science
Name: ____________________________ Date: ______________

Student Worksheet

The fictional town of Quorley sends its health inspector to check homes for cross-connections. A cross-connection is any place where drinking water plumbing can touch water that is not safe to drink, such as a hose lying in a pool or a faucet under the water in a full sink. When pressure in the street main drops, water can be pulled backward through that connection and into the pipes of the house.

Two protections stop this. An air gap is open space between the end of the faucet and the highest water level below it. If pressure drops, the faucet can pull in only air across that gap, not the water below. A vacuum breaker is a small fitting screwed onto an outdoor faucet, called a hose bibb, that lets air in and stops the backward pull.

Quorley's plumbing code, in our scenario, uses the common air gap rule: the gap must be at least 2 times the width of the faucet opening, and never less than 1 inch.

Show your work for every item.

  1. A kitchen faucet has an opening 0.5 inch across. Using the two-times rule, what is the minimum air gap for that faucet?

  2. A laundry sink faucet has an opening 0.75 inch across. What is its minimum air gap?

  3. A shop sink faucet has an opening 1.25 inches across. What is its minimum air gap?

  4. In this rule, the minimum air gap is proportional to the width of the faucet opening. What is the constant of proportionality?

  5. The kitchen faucet from item 1 ends 2 inches above the rim of the sink. Does that faucet meet the Quorley minimum?

  6. The laundry sink faucet from item 2 ends 0.5 inch above the rim. How many inches short of its minimum air gap is it?

  7. A garden hose is left with its end lying under the water while a wading pool fills. Is that a cross-connection risk, and what is the fix?

  8. A hose with a sprayer full of weed killer stays screwed onto the outdoor faucet all week. Is that a cross-connection risk, and what is the fix?

  9. A hose runs from the laundry sink into a barrel of soapy water, with the hose end below the surface. Is that a cross-connection risk, and what is the fix?

  10. The town flushes a hydrant on the street and pressure in the main drops for a minute. Explain what could happen at the house in item 7 while the hose is still lying in the pool.

  11. In our scenario, the Quorley inspector checked 40 homes and found at least one cross-connection risk at 14 of them. What percent of the checked homes had a risk?

  12. Explain why a cross-connection at one house can matter to the neighbors on the same street.

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: 1 inch.
    2 times 0.5 inch equals 1 inch, which also meets the rule's floor of 1 inch.

  2. Answer: 1.5 inches.
    2 times 0.75 inch equals 1.5 inches.

  3. Answer: 2.5 inches.
    2 times 1.25 inches equals 2.5 inches.

  4. Answer: 2.
    For openings of 0.5 inch or wider, the minimum gap is the opening width multiplied by 2, so the constant of proportionality is 2. Below that width, the 1-inch floor applies instead. Written as an equation, gap equals 2 times diameter.

  5. Answer: Yes. The minimum for a 0.5-inch opening is 1 inch, and this faucet ends 2 inches above the rim, so it clears the minimum by 1 inch.

  6. Answer: 1 inch.
    The minimum is 1.5 inches and the faucet ends only 0.5 inch above the rim. 1.5 minus 0.5 equals 1 inch short.

  7. Answer: Yes, this is a risk. Pool water can be pulled up the hose into the house plumbing. The fix is to keep the hose end above the water line so there is an air gap, and to add a vacuum breaker to the outdoor faucet.

  8. Answer: Yes, this is a risk. The sprayer holds weed killer that is connected to the plumbing through the hose. The fix is a hose bibb vacuum breaker on the faucet, and disconnecting the sprayer when the job is done.

  9. Answer: Yes, this is a risk. Soapy water can be pulled back through the hose into the laundry sink plumbing. The fix is to raise the hose end above the water in the barrel so there is an air gap.

  10. Answer: Pool water could be siphoned backward into the home's pipes. When main pressure drops, the higher pressure is now inside the pool end of the hose, so water moves toward the low-pressure side and carries whatever is in the pool with it.

  11. Answer: 35 percent.
    14 homes divided by 40 homes equals 0.35, which is 35 percent.

  12. Answer: Water pulled backward does not stop at the property line. It can travel from the house plumbing into the service line and reach the street main that supplies every home on the block, which is why cross-connection rules apply to private property.

Differentiation

Support

Give these students the first air gap worked as a model and a labeled drawing showing the faucet opening, the rim, and the gap between them. Allow them to answer items 7 through 9 by circling the fix from a short list rather than writing it, and let them stop after item 11.

Extension

Ask students to walk their own kitchen and bathroom in their heads, list two fixtures, estimate each opening width, and state whether the gap they picture would pass the rule. Have them write one sentence explaining why a laundry tub is riskier than a bathroom sink.

ELL supports

Pre-teach "hose bibb," "air gap," and "backflow" with three simple drawings, one per term, labeled with arrows showing the direction water moves. Provide a sentence frame for items 7 through 9: "This is a risk because ___. The fix is ___."

Extensions

Students can look for the vacuum breaker on an outdoor faucet at school or at home and sketch what they find, since many older faucets have none. A follow-up discussion can cover why irrigation systems, pools, and fire sprinklers usually need a larger backflow device that a certified technician tests once a year.