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What Is a One Part Per Million Solution?

Author(s): Nancy P. Moreno, PhD, Barbara Z. Tharp, MS, and Judith Dresden, MS.

Let’s Talk About It

Review the fractions represented on the worksheet, "What Does One in a Million Look Like?" Make sure that students understand the concentration in Cup 6 is one part in one million. 

Each of cups 2–6 holds a solution that is 10 times more diluted that the solution in the preceding cup. Ask, Is there another way that we could make a mixture with one part in one million? Of course, we could add one drop of food coloring to 999,999 drops of water. 

Hold up a glass of tap water. Ask students, Could our drinking water contain tiny amounts of other substances? Follow up by asking, What might those tiny things be? Possible answers could include: minerals, microorganisms (germs), or chemicals. Ask, Are all of these things harmful? 

Help students to understand that almost no water, except in a laboratory, is completely pure. Although it may look clear and clean, water often contains many types of chemical and biological materials. Most of these are harmless, especially in tiny quantities. In fact, even water that comes from crystal clear wilderness sources, or “natural” spring water sold in stores, contains dissolved minerals and other substances. 

Point out, though, that some pollutants can be harmful to humans (for example, heavy metals like lead and mercury, pesticides, and some industrial chemicals), even in tiny amounts measurable only in parts per million or parts per billion. Mention that certain city, county, state and federal agencies test drinking water for potentially harmful chemicals, and that the Environmental Agency (EPA) sets limits for acceptable amounts of potentially harmful chemicals in drinking water. Ask students, Why is it important to test our drinking water?


Funded by the following grant(s)

National Institute of Environmental Health Sciences, NIH

National Institute of Environmental Health Sciences, NIH

The Environment as a Context for Opportunities in Schools
Grant Numbers: 5R25ES010698, R25ES06932


Houston Endowment Inc.

Houston Endowment Inc.

Foundations for the Future: Capitalizing on Technology to Promote Equity, Access and Quality in Elementary Science Education