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Water Quality — Reading Comprehension

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MS-ESS3-1
MS-ESS3-3

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This middle school science reading passage covers the topic of water quality, aligned with NGSS standards MS-ESS3-1 and MS-ESS3-3. Students learn why clean water is essential for drinking, agriculture, industry, and ecosystems, and how different types of pollutants (such as pathogens, nutrients, toxic chemicals, sediments, and heat) affect freshwater sources. The passage explains the difference between point and nonpoint source pollution, how scientists measure water quality using dissolved oxygen, pH, turbidity, and biological indicators, and the role of water treatment and regulations like the Clean Water Act. Real-world examples and scientific thinking are integrated, helping students understand how protecting water quality supports public health and the environment. This resource includes audio integration for accessibility, a glossary, comprehension and writing activities, and graphic organizers to deepen understanding.

CONTENT PREVIEW

Vibrant green algae bloom in a natural waterway, showcasing environmental impact on aquatic ecosystems. — Eutrophication—the overgrowth of algae. Image by Victor Moragriega / Pexels.

Water quality determines whether freshwater can safely support drinking, farming, industry, and natural ecosystems. In many communities, water from rivers, lakes, or underground aquifers must meet specific standards to be safe for humans, animals, and plants. However, pollutants can enter water sources from many places, sometimes making water unsafe or damaging to the environment. Understanding what affects water quality and how we measure it helps people, governments, and scientists protect this critical resource.

How Pollutants Enter Waterways
Some pollutants come from point sources, which are single, identifiable places such as a factory outfall pipe or a sewage treatment plant. Other pollutants arrive through nonpoint sources, which are widespread and not easily traced, like fertilizer runoff from farms or oil washed off city streets by rain. The types of pollution include pathogens (harmful bacteria and viruses), nutrients (nitrogen and phosphorus, which can cause eutrophication—the overgrowth of algae), toxic chemicals (like pesticides and heavy metals), sediment (soil particles that cloud water), and thermal pollution (heated water from factories or power plants). For example, when excess nutrients enter a lake, they can cause algae blooms that reduce oxygen in the water, killing fish and making the water unsafe for recreation.

Measuring and Monitoring Water Quality
Scientists and water managers use several methods to assess water quality. They measure dissolved oxygen to see if water can support fish and other aquatic life. The pH tells us if water is acidic or basic, and turbidity indicates how clear or cloudy the water is. Chemical tests detect contaminants such as nitrates, phosphates, or heavy metals. Biological indicators—like the presence or absence of certain insects or fish—reveal long-term water health. For instance, a river with many mayflies usually has good water quality, while their absence can signal pollution.

Protecting and Treating Water
Communities use different methods to ensure water is safe. Municipal water treatment systems use filtration to remove sediment, and chlorination or other disinfectants to kill pathogens. Laws like the Clean Water Act set standards for pollutants and require regular monitoring. Best practices such as preserving wetlands, reducing fertilizer use, and managing stormwater runoff help prevent pollution before it starts. Healthy wetlands filter pollutants naturally, supporting both wildlife and people.

Clean water is essential for all living things. By understanding the sources of pollution, how to measure water quality, and ways to prevent contamination, we can help protect freshwater for future generations. This connects to broader scientific ideas about how human activities affect Earth's systems and the importance of sustainable resource management.

Interesting Fact: Less than 1% of Earth's water is easily available as freshwater for people, animals, and plants!

What is the main reason communities care about water quality?

To make sure water is safe for people, animals, and the environmentTo increase the number of factories near riversTo make water look more colorfulTo use more fertilizer in farming

Which is an example of point source pollution?

Runoff from many farms after rainA pipe from a factory releasing chemicalsOil spread from cars on roadsFertilizer carried by wind

What happens during eutrophication?

There is too much oxygen in the waterAlgae grow very quickly and reduce oxygenFish grow larger than normalThe water becomes colder

What is measured by turbidity tests?

How clear or cloudy the water isHow much oxygen is in the waterThe water's temperatureThe number of bacteria

What is a nonpoint source of pollution?

A city stormwater drainA single sewage plantRunoff from lawns and streets over a large areaA leaking oil tanker

What do municipal water treatment systems use to kill pathogens?

Heavy metalsNutrientsChlorinationSediment

A river with many mayflies probably has...

Bad water qualityGood water qualityNo dissolved oxygenHigh levels of toxic chemicals