Reading passage Grade 8 English Language Arts
Why Chalkstone Bend's Water Leaves a White Ring
A grade 8 informational passage on hard water in a fictional limestone town, tracing calcium from rock to kettle and weighing two ways to soften it.
Objectives
- Students will trace the chain of causes that puts dissolved calcium in a town's tap water.
- Students will explain the difference between a nuisance problem and a health problem.
- Students will infer why a household softener moves a cost rather than removing it.
Vocabulary
- Ion exchange
- A water treatment method that swaps unwanted charged particles in the water for harmless ones held on tiny resin beads. It is used to remove PFAS and to soften hard water.
Also: hard water, dissolved, scale, nuisance, softening
Teacher overview
Hard water is one of the few water topics students can verify in their own kitchens, which makes it a useful text for practicing inference about causes. The passage follows calcium from limestone to a kettle in a fictional town, then sets up a decision the water department has to make. It also corrects a common misconception, which is that anything the water department removes must be a health threat. Hardness is a nuisance, and the passage keeps that distinction in view while showing that a nuisance can still be expensive.
Passage
Chalkstone Bend is a fictional town of about 6,000 people. It sits on a thick bed of limestone. Every drop of its drinking water comes from wells drilled into that rock. The water is clear, tested, and safe to drink, and it leaves a white ring in every kettle in town.
Rain does not stay pure for long. As it falls, it picks up a little carbon dioxide from the air. More carbon dioxide waits in the soil, where roots and tiny organisms give it off. Water and carbon dioxide together make a weak acid. That weak acid is not strong enough to hurt a person, but it is strong enough to work on stone.
Limestone is mostly calcium carbonate. When the slightly acid water seeps through cracks in the rock, it dissolves a small amount of calcium. It picks up magnesium in the same way. Neither one can be seen in a glass. Well water from Chalkstone Bend looks exactly like well water from a granite hillside. What has changed is what the water is carrying.
Water that carries a lot of dissolved calcium and magnesium is called hard water. Hardness is not covered by a health rule. No agency sets a safety limit for it, and no doctor tells a family to stop drinking it. Hardness belongs to a group of water problems that operators call nuisances, meaning problems people notice rather than problems that make them sick.
Residents notice this one in three ways. Soap does not lather well, because the calcium grabs the soap before the soap can make bubbles. A white crust builds up on shower doors, faucets, and the inside of kettles. That crust is called scale. Scale also forms inside water heaters, where it coats the heating element like a shell. A coated element has to run longer to heat the same tank, so the household pays for the coating on its power bill.
The fictional water department has two ways to deal with hardness, and they land the cost in different places. The first is to soften the water at the plant. Operators add lime, which raises the water's pH and pushes the dissolved calcium to form solid grains that settle out of the water. The method works, and it is old and well understood. It also produces truckloads of wet solids that someone has to haul away, and it raises the bill for every customer, including the ones who never minded the white ring.
The second way is to leave the water alone and let households buy their own softeners. A household softener uses ion exchange. Water flows through a tank of small plastic beads that hold sodium. The beads trade their sodium for the calcium and magnesium in the water, and the household gets soft water for a while. When the beads fill up, the unit rinses them with salt water and sends the rinse down the drain.
The rinse water matters as much as the soft water the unit produces. It carries chloride, and chloride is one of the few things a wastewater plant cannot easily remove. Whatever goes down that drain leaves the plant later and enters the creek below town. A softener in a basement does not end the town's hardness problem. It moves the problem to the creek and hands the bill to whoever has to answer for the creek.
The department has not chosen yet. It plans to soften the water from one well for a year, measure what the change costs, and publish the numbers before the council votes.
Questions
- Where does Chalkstone Bend get its drinking water?
- According to the passage, what two things combine to make the weak acid that dissolves limestone?
- The passage calls hardness a nuisance. Explain what operators mean by that word, using the passage.
- Trace the chain of causes that puts calcium in a Chalkstone Bend kettle. Use at least three details from the passage.
- The passage says a household softener moves the problem instead of ending it. Explain that claim using the strongest evidence in the text.
- A resident says the white ring has never bothered her, so the town should do nothing. Using the passage, give one reason she might still be paying for hard water.
- Why might the department test softening on one well for a year instead of changing the whole system at once?
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: From wells drilled into the limestone the town sits on. The passage states that every drop of the town's drinking water comes from those wells.
- Answer: Water and carbon dioxide. The passage says rain picks up carbon dioxide from the air and from the soil, and that the two together make a weak acid.
- Answer: A nuisance is a problem people notice rather than one that makes them sick. The passage says no agency sets a safety limit for hardness and no doctor tells families to stop drinking the water.
- Answer: Rain picks up carbon dioxide from the air and soil, which makes the water a weak acid. That water seeps through cracks in the limestone and dissolves calcium and magnesium. The wells pull that water up, and the calcium stays in it until the kettle boils the water away and leaves the calcium behind as scale.
- Answer: Because the softener does not destroy anything. The passage says the beads trade sodium for calcium and are then rinsed with salt water, and that the rinse carries chloride the wastewater plant cannot easily remove, so the chloride leaves the plant and enters the creek below town.
- Answer: Scale builds up inside her water heater and coats the heating element, so the unit has to run longer to heat the same tank. The passage says the household pays for that coating on its power bill even if nobody minds the ring.
- Answer: Answers will vary but should rest on the passage's statement that the department plans to measure what the change costs and publish the numbers before the council votes. A strong answer notes that softening the whole system would raise every customer's bill and create solids to haul away, so testing one well gives the council real figures before it commits the town.
Differentiation
Support
Give these students a five-box cause and effect chain labeled rain, soil, limestone, well, and kettle, and have them place one sentence from the passage in each box before answering. Reduce the required questions to 1, 2, 3, and 6.
Extension
Ask students to write the one-page notice the fictional department would mail with the pilot results, explaining to customers who never minded the white ring why they are being asked to help pay for softening, using only reasoning the passage supplies.
ELL supports
Pre-teach "dissolve," "scale," "nuisance," and "soften" with a labeled drawing of a kettle before and after the white crust forms. Read the first three paragraphs aloud before independent reading, and allow questions 1 and 2 to be answered in short phrases.
Extensions
Students compare this passage with a short product description for a household softener that they write themselves, then list two facts from the passage that a seller would be unlikely to include and explain why.