Water Quality-Total Dissolved Solids

• Learn the difference between total dissolved solids and total suspended solids.
• Learn how water quality is related to total dissolved solids.
• Compare TDS levels for streams, lakes, and rivers in your local area.
• Compare TDS levels to standard samples and to other well known locations in the United States.

This activity can be used as a lab activity in an introductory geoscience course that contains a discussion of ocean salinity, hydrology and/or water quality.

Instructors can also easily incorporate aspects of this activity into an interactive lecture.

This activity requires a microcomputer, multi-sensor interface, and conductivity probe. The specific activity is included in Earth Science With Computers by Robyn Johnson, Gretchen Stahmer DeMoss, and Richard Sorensen published by Vernier Software (more info) , with a site license for $45.00. The complete activity in pdf format can be viewed at Water Quality-TDS (Total Dissolved Solids) The cost of the interface and conductivity probe are $220 and $89 respectively.

Students can also use a graphing calculator with the interface and conductivity probe.

Comparable equipment can also be purchase from Pasco Scientific.

This activity will take approximately 2 hours to complete in a lab setting with some extra time possibly needed for students to summarize their results. The activity description at Water Quality-TS (Total Solids) comes complete with two pages of Teacher information.

Doing parts or all of this activity as an interactive lecture is also an option.

This activity can also be done in three phases and in conjunction with a water quality pH activity which is also in Earth Science With Computers . First, a protocol is established for water sample collection either in lecture or as part of a lab activity. Next, students go out on their own or in small groups to collect water samples from different water bodies in their local area. Finally, students perform measurements of TDS and pH in the lab followed by a summary of all results and a debriefing.

The activity comes with very specific instructions. Assessment is most easily accomplished by reviewing student results and with a follow up discussion of all results. Having students design their own experiment for an "Extension" investigation can also help you better assess their ability to synthesize what they have learned and apply it to a slightly different situation.

Vernier Software (more info) has several other sample geoscience labs from Earth Science With Vernier available in pdf format as examples at other examples . These include "Where is North", "Reflection and Absorption of Light", and "Comparing Sunscreens"

Pasco Scientific has about 13 online lab activities available for free. These are mostly geared towards high school students but can easily be modified for an introductory college level course as either a laboratory activity, a special project, or an interactive lecture example.