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Reading passage Grade 8 English Language Arts

Twenty-Four Hours After Flintlow's Bad Water Sample

A grade 8 informational passage following a fictional town's routine coliform sample from the tap to the county lab, and the decisions an operator makes while waiting.

Objectives

  1. Students will sequence the steps a routine bacteria sample goes through from tap to lab result.
  2. Students will explain the difference between an indicator organism and a harmful one.
  3. Students will infer why the repeat sampling rule places samples upstream and downstream.

Vocabulary

Chlorine residual
Chlorine residual is the small amount of chlorine still left in the water after it leaves the treatment plant. It keeps protecting the water from germs all the way to your faucet.
Boil water advisory
A public notice telling people to boil tap water before drinking it because germs may have entered the pipes, often after a main break or a loss of pressure.

Also: coliform, indicator, incubator, repeat sample

Teacher overview

Water testing is usually presented as a result rather than as a process, which hides the reasoning that makes the result useful. This passage follows one routine bacteria sample in a fictional town through collection, the lab, and the day of waiting that follows a positive result. It is built around a distinction students regularly miss, which is that the bacteria the test looks for are mostly harmless. They are watched because they signal that something else could get in, and the questions ask students to hold that difference between an indicator and a hazard.

Twenty-Four Hours After Flintlow's Bad Water Sample — Grade 8 English Language Arts
Name: ____________________________ Date: ______________

Passage

Flintlow is a fictional town of about 3,200 people. Like every public water system, it has a sampling plan. The plan lists the taps where samples must be collected and the month each one is due. Dean Achebe, the town's operator, works the list on the first Tuesday of every month.

He starts at the tap behind the fire station. The bottle he uses is sterile and holds a small tablet that cancels the chlorine in the water, so the bacteria in the bottle stop being killed the moment the sample is taken. He wipes the tap, runs the water for a few minutes, and fills the bottle to the line without touching the rim. Then he writes the time on the label and sets the bottle in a cooler of ice. The sample has a holding time. If it sits too long before the lab starts the test, the result no longer counts, and he has to drive back and collect it again.

At the county lab, a technician pours the sample into a vessel with a powdered growth medium and sets it in an incubator. The incubator holds the sample near body temperature for about twenty-four hours. If total coliform bacteria are living in the water, they feed on the medium and the liquid changes color. A technician then holds the vessel under an ultraviolet lamp. If the sample glows, E. coli is present as well.

Those two results do not mean the same thing. Total coliform bacteria live in soil, on plants, and in surface water, and most of them do not make anyone sick. Operators watch them because they are easy to grow and easy to find. A positive total coliform result says that a path may have opened somewhere between the plant and the tap. It does not say that anything harmful has traveled that path. E. coli is the second signal, and it is the serious one, because E. coli lives in the intestines of animals and people. Finding it points toward waste rather than toward soil.

When the fire station sample came back positive for total coliform, Dean had a day of work and no answer yet. The rules required repeat samples within twenty-four hours: one at the same tap, one at a tap a short distance upstream in the pipe network, and one a short distance downstream. Three samples in a line can show whether the problem sits at that one faucet or somewhere in the main that feeds it.

While the repeats sat in the incubator, he worked the other evidence. He checked the chlorine residual at several hydrants, because most systems keep a residual somewhere between 0.2 and 2.0 mg/L in their pipes, and a low reading in one direction would point him toward that part of town. He pulled the pressure charts to see whether the system had lost pressure, which can pull outside water into a pipe through a crack. He asked the crew whether anyone had repaired a main or opened a hydrant near the fire station that week.

The repeats came back clean the next afternoon. Flintlow filed a short assessment naming the most likely cause, which was a sampling tap that had not been used in weeks, and the town replaced the tap. Had the repeats come back positive, the town would have begun a fuller assessment of its system with the state. Had E. coli appeared, it would have notified the state that day and warned customers, most likely with a boil water advisory.

None of the waiting can be shortened. The bacteria need the same twenty-four hours whether the news is good or bad, which is why the schedule matters more than the speed.

Questions

  1. What does Dean do to the sample bottle after he fills it?
  2. According to the passage, what happens inside the incubator, and about how long does it take?
  3. How does the lab tell whether E. coli is present rather than only total coliform?
  4. The passage describes total coliform bacteria as a signal rather than a danger. Explain what that means, using details from the text.
  5. The repeat samples are collected at three places rather than one. Explain what the three locations together can show that a single repeat could not.
  6. Why does Dean check chlorine residual and pressure records while he is waiting for the repeat results?
  7. The passage ends by saying the schedule matters more than the speed. Explain what that ending suggests about how a small system protects its customers.

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: He writes the time on the label and puts the bottle in a cooler of ice. The passage says the sample has a holding time and will not count if the lab starts the test too late.
  2. Answer: The sample is held near body temperature for about twenty-four hours with a growth medium, and the liquid changes color if total coliform bacteria are living in the water.
  3. Answer: A technician holds the vessel under an ultraviolet lamp. If the sample glows, E. coli is present in addition to total coliform.
  4. Answer: Most total coliform bacteria live in soil, on plants, and in surface water and do not make people sick. Operators watch them because they are easy to grow and find, so a positive result says a path may have opened between the plant and the tap rather than that something harmful came through it.
  5. Answer: The three samples sit in a line along the pipe network, one at the same tap and one on each side of it. Together they can show whether the problem is limited to that one faucet or whether it reaches the main that feeds the area, which a single repeat at the same tap could not distinguish.
  6. Answer: Because those records point toward a cause while the lab work is still running. A low chlorine residual in one direction would suggest which part of town to look at, and a recorded loss of pressure could explain how outside water was pulled into a pipe through a crack.
  7. Answer: Answers will vary but should rest on the passage's statement that the incubation cannot be shortened. A strong answer explains that because no result can arrive faster than a day, a small system protects customers by sampling on a fixed plan, keeping records that narrow the cause, and having the repeat and advisory steps decided in advance.

Differentiation

Support

Give these students a six-step flow strip labeled collect, cool, deliver, incubate, read, and repeat, and have them place one sentence from the passage under each step before answering. Reduce the required questions to 1, 2, 3, and 6.

Extension

Ask students to write the two-paragraph memo Dean would send the council explaining why the positive result did not lead to a boil water advisory, using only the reasoning the passage supplies about indicators, repeat samples, and the assessment.

ELL supports

Pre-teach "sterile," "sample," "incubator," and "residual" with a labeled photograph or sketch of a sample bottle, a cooler, and an incubator tray. Read the fourth paragraph aloud twice, since the indicator idea carries the rest of the text, and allow questions 1 through 3 to be answered in short phrases.

Extensions

Students write the one-sentence entry Dean would put in the plant log for each day the passage describes, then compare their entries with a partner's and discuss which details a log keeps and which it leaves out.