Is It Clean or Just Unseen? Dirty Water and the Naked Eye


In this experiment, serial dilution of a contaminated water source is examined for turbidity and bacterial cell count. Because chemical and microbial contaminations are not always visible to the naked eye, the microbial presence will be brought to the attention of the learner by use of viable plate counts.

Intended Audience

Grades 9-12

Learning Objectives

At the completion of this activity the learner will be able to successfully perform serial dilutions as well as be able to calculate the corresponding concentration of the dilutions. The student will also have knowledge of how to conduct a bacterial cell count and thus bacterial concentrations.

Necessary Student Background

Students should be equipped with the skill set and knowledge of using transfer pipettes and compound light microscope (if you choose to use one). They should also be able to use mathematical concepts to prepare dilutions.


Contamination, Serial Dilution, Turbidity, Microorganism Bacterial, Cell Count

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Is It Clean or Just Unseen? Dirty Water and the Naked Eye (12 pages)