Water Quality: Total Dissolved Solids

Figure from experiment 9C from STEM with Vernier and LEGO MINDSTORMS NXT


Solids are found in bodies of water in two forms, suspended and dissolved. Suspended solids include silt, stirred-up bottom sediment, decaying plant matter, or sewage-treatment effluent. Dissolved solids are ions introduced to water from salts, acids, bases, hard-water minerals, or soluble gases that ionize in solution. Suspended solids will not pass through a filter, whereas dissolved solids will.

In this experiment, you will measure the total dissolved solids (TDS) of several water samples using a Vernier Conductivity Probe. You will learn to convert conductivity values in mS/cm to TDS values in mg/L. The Conductivity Probe can determine the ability of dissolved salts and their resulting ions to conduct an electrical current. The test described here will not tell you the specific ion responsible for the increase or decrease in TDS. It will simply give a general indication of the level of dissolved solids in the water sample.


In this experiment, you will

  • Use a computer and an NXT to measure total dissolved solids.
  • Learn to use a conversion factor.
  • Compare water from different sources.

Sensors and Equipment

This project/activity requires each of the following Vernier sensors and equipment (unless otherwise noted):

Additional Requirements

You will also need NXT Sensor Adapter and a LEGO MINDSTORMS NXT robotics system.

Download Project/activity Preview

The student-version preview includes:

  • Step-by-step instructions for computer-based data collection
  • List of materials and equipment

The preview does not include essential teacher information, safety tips, or sample data. We strongly recommend that you purchase the book for classroom use.

Download Preview

Standards Correlations

No standards correlations for this experiment.

Project/activity 9C from STEM with Vernier and LEGO MINDSTORMS NXT Lab Book

<em>STEM with Vernier and LEGO MINDSTORMS NXT</em> book cover

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Included in the Lab Book

Vernier lab books include a CD with word-processing files of the student instructions, essential teacher information, suggested answers, sample data and graphs, and more.

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