Writing prompt Grade 10 Science
Halgrave's Water Audit: Explaining the Missing Third
A grade 10 science explanatory prompt where students use a town water audit to explain apparent losses, real losses, and how three repairs change river withdrawals.
Objectives
- Students will explain the difference between apparent losses and real losses in a water audit.
- Students will use audit figures to describe how much water never reaches a paying customer.
- Students will explain how each proposed repair changes the volume pumped from the river.
Vocabulary
- Water audit
- A careful check of where water goes, either in a home or across a whole water system. Audits find leaks and waste so they can be fixed.
- Non-revenue water
- Water that a utility treats and pumps but never gets paid for. Most of it escapes through leaks in old pipes, and some is lost to broken meters or theft.
Also: apparent loss, real loss, pressure management
Teacher overview
Every utility treats more water than it bills for, and the gap between the two numbers has a name and a standard accounting method. A water audit sorts that gap into water the utility gave away on purpose, water it delivered but failed to measure, and water that leaked out of the pipes. This prompt gives students a full audit for a fictional town and asks them to explain it to residents, including the distinction that decides how much water the town keeps in its river, which is that replacing meters recovers revenue without lowering the volume the plant must treat.
Prompt
Background: The fictional town of Halgrave draws its water from the Pilbury River. The river runs low in August, and the state has asked the town to reduce its summer withdrawal. Halgrave completed its first full water audit last year. Every figure below comes from that fictional audit.
The plant produced 620,000,000 gallons over the year. Customers were billed for 415,000,000 gallons. The audit sorted the remaining water into three categories.
Authorized unbilled use came to 18,000,000 gallons. This is water the town used on purpose without charging anyone, including fire fighting, hydrant testing, and flushing mains.
Apparent losses came to 47,000,000 gallons. This is water that reached a customer but was never counted, usually because an old meter spins slowly or a billing record is wrong. The water was used. The town simply was not paid for it.
Real losses came to 140,000,000 gallons. This is water that left the pipes through leaks, joints, and main breaks, and never reached anyone.
Halgrave's engineers have proposed three measures.
An acoustic leak survey of the distribution mains would cost $180,000 and is expected to find leaks losing about 40,000,000 gallons a year.
Replacing 3,200 residential meters older than twenty years would cost $960,000 and is expected to capture about 25,000,000 gallons a year of apparent loss.
Pressure management would cost $140,000. Control valves would lower nighttime pressure in the high zone from 88 psi to 62 psi, which is expected to cut real losses by about 30,000,000 gallons a year.
Writing task: Write an explanatory article for the Halgrave utility newsletter. Explain what the audit measured and what each category means. Use the figures to show how much of the town's water never reached a paying customer. Then explain how each of the three measures would change the amount of water Halgrave has to pump out of the Pilbury River. Write for a reader who pays a water bill and has never seen an audit.
Planning Organizer
| Category | Your notes |
|---|---|
| What a water audit measures, in one sentence | |
| Authorized unbilled use: definition and figure | |
| Apparent losses: definition and figure | |
| Real losses: definition and figure | |
| Total water never billed, and how you calculated it | |
| Effect of the leak survey on river withdrawal | |
| Effect of the meter replacement on river withdrawal | |
| Effect of pressure management on river withdrawal | |
| Closing sentence for a newsletter reader |
From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.
Exemplar & Rubric
Exemplar response:
Last year the Halgrave treatment plant produced 620,000,000 gallons of drinking water, and the town billed customers for 415,000,000 gallons of it. The difference, 205,000,000 gallons, is about a third of everything the plant made. A water audit exists to explain that difference, and the audit sorts it into three very different kinds of water.
The smallest category is authorized unbilled use, which came to 18,000,000 gallons. That is water the town used on purpose and chose not to charge for, such as fighting fires, testing hydrants, and flushing mains to keep the water fresh. The second category is apparent losses, 47,000,000 gallons. That water reached customers and was used normally, but old meters and billing errors kept it from being counted. The third and largest category is real losses, 140,000,000 gallons, which escaped through leaking joints and broken mains and never reached anyone at all.
The distinction between those last two categories matters more than it sounds. Replacing 3,200 old meters at a cost of $960,000 would capture about 25,000,000 gallons a year of apparent loss. Every one of those gallons is already being delivered and used, so the meters would recover revenue without lowering the amount of water the plant has to treat. The plant would still pump the same volume out of the Pilbury River.
The other two measures work on the river directly. The acoustic leak survey, at $180,000, is expected to find leaks that lose about 40,000,000 gallons a year, and pressure management, at $140,000, is expected to cut another 30,000,000 gallons by lowering nighttime pressure in the high zone from 88 psi to 62 psi. Together those measures address 70,000,000 gallons of the 140,000,000 gallons Halgrave now loses to leaks, or half the total. Water that never leaks out is water the town never has to pump, so those two projects are the ones that reduce the August withdrawal the state has asked Halgrave to cut.
Rubric:
| Criterion | Emerging | Developing | Proficient | Advanced |
|---|---|---|---|---|
| Explanation of the audit | Does not explain what the audit measures | Names the categories without defining them | Defines all three categories accurately and in plain language | Defines all three categories and explains why the audit separates them |
| Use of the figures | Uses no figures from the background | Repeats a figure without interpreting it | Uses several figures and calculates the total never billed | Uses figures accurately, calculates the total, and expresses at least one as a share of production |
| Apparent versus real losses | Treats the two as the same thing | States they differ without explaining the consequence | Explains that meter work recovers revenue while leak work reduces pumping | Explains the distinction and applies it correctly to all three proposed measures |
| Organization and conventions | Ideas disconnected; errors block meaning | Some organization; errors are noticeable | Clear paragraphs, plain language, few errors | Purposeful structure written for a general reader, virtually error-free |
Differentiation
Support
Give students a completed organizer row for authorized unbilled use as a model, and provide the sentence frame "This category means ___, and last year it came to ___ gallons." Allow the article to be written as four labeled sections rather than flowing paragraphs.
Extension
Ask students to add a short closing paragraph recommending which measure the town should fund first, with a reason drawn from the audit. Require them to name one piece of information the audit does not provide that would strengthen the recommendation.
ELL supports
Pre-teach "audit," "billed," "apparent," and "leak" with a simple flow diagram showing water leaving the plant and splitting into billed water, unbilled use, uncounted water, and leaks. Allow the organizer to be completed in phrases, and permit a first draft in a student's home language.