Water quality is one of the most important factors in a healthy ecosystem. Clean water supports a diversity of plants and wildlife. Though it may seem unrelated at first, our actions on land affect the quality of our water. Pollutants, excessive nutrients from fertilizers, and sediment frequently get carried into local lakes and rivers via runoff from urban areas or agricultural fields. This lesson considers the factors that influence water quality by observing and evaluating several water samples. Grade level: 4-8^th grades Performance Expectations:

• 2-PS1-1 Matter and its Interactions: Plan and conduct an investigation to describe and classify different samples of water based on their chemical and observable properties including temperature, pH and turbidity.
• 2-PS1-2 Matter and its Interactions: Analyze data from the testing of the water samples to determine which materials have the properties that are suited for certain purposes such as drinking, swimming or cooking.

For alignment, see: Water Quality NGSS Summary

Objectives

• Develop criteria for the quality of water and understand that there is more to water quality than “meets the eye.”
• Engage in a sample of water quality tests used by scientists.
• Explain how water quality in both groundwater and surface systems is impacted by land use decisions.
• Classify solutions as acidic or basic, given their pH, and classify substances by their chemical properties (flammability, pH, acid-base indicators).
• Use tools and equipment appropriate to scientific investigations and make accurate measurements with appropriate units.
• Identify the need for evidence in making scientific decisions and then use data and samples as evidence to separate fact from opinion.

Background

Scientists measure a variety of properties to determine water quality. These include temperature, acidity (pH), dissolved solids (specific conductance), particulate matter (turbidity), dissolved oxygen, hardness and suspended sediment. Each reveals something different about the health of a water body. The result of a single measurement, however, is actually less important than monitoring changes over time. For example, if you measure the pH of the creek behind your house and find that it is 5.5, you might think it is acidic. But a pH of 5.5 might be “normal” for that creek. If the pH or the turbidity of your creek begins to change, however, something may be happening (probably upstream) that is affecting water quality. Taking routine measurements at scheduled intervals allows you to monitor overall changes in water quality. The following water properties are important in determining water quality:

• Temperature: Water temperature is important to fish and aquatic plants. Temperature can affect the level of oxygen, as well as the ability of organisms to resist certain pollutants. See: Water Temperature
• Acidity – pH: The measurement of pH is a measure of the amount of hydrogen ions (H+) present in a substance such as water. Knowing the amount of hydrogen in a substance allows us to judge whether it is acidic, neutral, or basic. See: Measuring pH
• Dissolved Oxygen: A small amount of oxygen, about ten molecules of oxygen per million molecules of water, is dissolved in water. Fish and microscopic organisms need dissolved oxygen to survive. See: Oxygen and Carbon Dioxide
• Turbidity: Turbidity makes the water cloudy or opaque. Turbidity is the amount of particulate matter (such as clay, silt, plankton, or microscopic organisms) suspended in water. See: Water Clarity
• Specific Conductance: Specific conductance measures the capacity of water to conduct an electrical current. It depends on the amount of dissolved solids, such as salt, in the water.
• Hardness: The amount of dissolved calcium and magnesium in water determines its “hardness.” Water hardness varies throughout the United States.
• Suspended Sediment: Suspended sediment is the amount of soil circulating in water. The amount depends in part on the speed of the water flow. Fast-flowing water can pick up and hold, or suspend, more soil than calm water

Activity

• Determining Water Quality Summary: Students make observations and measurements of several water samples. This activity helps students think about different ways to determine water quality. Time: 50 minutes or more