Science: Testing your Water

Abstract
Tucson, Arizona residents depend on groundwater as the main source of their drinking water. This water resource is particularly vulnerable to contamination due to the geology within the state of Arizona, rapid land use changes, and a rapidly growing population. In this lesson students will test the quality of their drinking water from several samples.

Objectives
Students will be able to:

use appropriate lab safety protocols
collect and perform basic chemical analysis on water samples
analyze data and create and interpret meaningful graphs to determine the impact of environmental pollutants on water quality

National Science Education Standards
Content Standard A: Science as Inquiry
COMMUNICATE AND DEFEND A SCIENTIFIC ARGUMENT.
Students in school science programs should develop the abilities associated with accurate and effective communication. These include writing and following procedures, expressing concepts, reviewing information, summarizing data, using language appropriately, developing diagrams and charts, explaining statistical analysis, speaking clearly and logically, constructing a reasoned argument, and responding appropriately to critical comments.

Content Standard F: Science in Personal and Social Perspectives
ENVIRONMENTAL QUALITY
Natural ecosystems provide an array of basic processes that affect humans. Those processes include maintenance of the quality of the atmosphere, generation of soils, control of the hydrologic cycle, disposal of wastes, and recycling of nutrients. Humans are changing many of these basic processes, and the changes may be detrimental not only to humans, but also the environment. [See Content Standard C (grades 9-12)]
Materials from human societies affect both physical and chemical cycles of the earth.

Teacher Background
Groundwater is the part of precipitation that seeps down through the soil until it reaches rock material that is saturated with water. Groundwater slowly moves underground, generally at a downward angle (because of gravity), and may eventually seep into streams, lakes and oceans. Groundwater is an important natural resource, especially in those parts of the country that do not have ample surface-water sources, such as the arid West, to provide inhabitants with the necessary water. It provides about 50% of the water delivered by the water department for use in Tucson homes, businesses and industries and provides drinking water for 99% of the rural population who receives their water from their own wells.

Tucson’s rapidly growing population requires a greater water source. Pima county’s population has increased over 26% from 1990-2000. This increasing population is not only requiring more water, but also land that once served as open flowing watersheds. These watersheds are being converted into housing complexes, shopping centers and roadways. The rapid changes in land use can have major effects on the flow of water through a watershed and strict building codes must be enforced to ensure public safety.

Arizona’s geology is unique with large deposits of rare and heavy metals. Some of these rare minerals (i.e. silver, copper) are what brought settlers west to Arizona. These metals are leached from the soil as the precipitation seeps down into the bedrock. This water can also be highly acidic from the various salts that are also dissolved as water passes through the ground. This natural contamination can make cleanup for water consumption much more difficult.

For water testing purposes, three different water samples should be collected (i.e. faucet, rural well, stream or canal) to show differences in water quality.

Related and Resource Websites

General Water & Arsenic
PULSE Arsenic Resource Page http://pulse.pharmacy.arizona.edu/resources/arsenic/teachers.htm
EPA on Safe Drinking Water http://www.epa.gov/safewater/mcl.html#mcls
National Groundwater Association http://www.ngwa.org/
ExToxNet on Testing Your Water http://extoxnet.orst.edu/faqs/safedrink/test.htm
Know when and how to test your water http://www.thisland.uiuc.edu/57ways/57ways_34.html

Tucson Water
Tucson Water: Teachers & Students http://www.ci.tucson.az.us/water/education.htm
University of Arizona Water Resources Research Center http://www.ag.arizona.edu/azwater/about.html

Activity
Each lab station should have the following:

three 50mL beakers
a wax pencil or Sharpie
a set of water quality test strips

The water samples, placed at the teacher’s table, should be in large (gallon-size) jugs labeled with sample #1, #2, and #3. Break the students into groups of three to four students. Each group should obtain 25mL each of the three samples.

Measuring the pH:
1. Wearing latex gloves, carefully dip the pH test strip into the water sample. Swirl for amount of time indicated on package. Remove the strip.
2. Match the color of the strip to the pH color chart on the test strip package.
3. Record the pH of the sample in your data table
4. Repeat for sample #2 and sample #3.

Testing water hardness:
1. Wearing latex gloves, carefully dip the water hardness test strip into the water sample. Swirl for amount of time indicated on package. Remove the strip.
2. Match the color of the strip to the hardness color chart on the test strip package.
3. Record the hardness of the sample in your data table.
4. Repeat for sample #2 and sample #3.

Testing total alkalinity:
1. Wearing latex gloves, carefully dip the total alkalinity test strip into the water sample. Swirl for amount of time indicated on package. Remove the strip.
2. Match the color of the strip to the alkalinity color chart on the test strip package.
3. Record the hardness of the sample in your data table.
4. Repeat for sample #2 and sample #3
.
Testing for nitrates and nitrites:
1. Wearing latex gloves, carefully dip the nitrate and nitrite nitrogen test strip into the water sample. Swirl for amount of time indicated on package. Remove the strip.
2. Match the color of the strip to the nitrate and nitrite nitrogen color chart on the test strip package.
3. Record the hardness of the sample in your data table.
4. Repeat for sample #2 and sample #3.

Testing for iron:
1. Wearing latex gloves, carefully dip the total iron test strip into the water sample. Swirl for amount of time indicated on package. Remove the strip.
2. Match the color of the strip to the total iron color chart on the test strip package.
3. Record the hardness of the sample in your data table.
4. Repeat for sample #2 and sample #3.

Testing for copper:
1. Wearing latex gloves, carefully dip the total copper test strip into the water sample. Swirl for amount of time indicated on package. Remove the strip.
2. Match the color of the strip to the total copper color chart on the test strip package.
3. Record the hardness of the sample in your data table.
4. Repeat for sample #2 and sample #3.

Testing for chlorides:
1. Wearing latex gloves, carefully dip the total chlorine test strip into the water sample. Swirl for amount of time indicated on package. Remove the strip.
2. Match the color of the strip to the total chlorine color chart on the test strip package.
3. Record the hardness of the sample in your data table.
4. Repeat for sample #2 and sample #3.

It is true that most water contains some contaminants mentioned above. Obviously, in the proper amounts, these contaminants are necessary, but what are the proper/safe amounts? How much is too much? To understand the limitations of the EPA, you must understand a few of their terms.

Parts per million: ppm: 1mg of contaminant in 1L of water
Parts per billion: ppb: 1mg of contaminant in 1000L of water
Maximum Contaminant Level: MCL: the highest amount of contaminant that is allowed in the water at any given time
National Primary Drinking Water Regulations: NPDWRs: the legally enforceable standards applied to drinking water

Here is a short table of some contaminants, their MCL values, and health risks involved.

Contaminant	MCL	Health Risk
Chloride	4.0 ppm	Eye/nose irritation, stomach discomfort
Copper	1.3 ppm	Gastrointestinal distress
Iron	0.3 ppm*	Metallic taste; reddish or orange staining
Nitrate	10.0 ppm	Danger to infants: shortness of breath
pH	6.5-8.5	Stomach irritation
Hardness	0-50 soft water, 51-120 moderately hard, 121-150 hard, 251 and up very hard

* Secondary drinking water regulations.

After determining quality of the samples, check off in your data chart safe samples.

Conclusion:
Once you have decided which samples you believe are safe to drink, find out from your instructor where each water sample originated and prepare a report for your teacher comparing the water quality of each and assessing the suitability of the water for drinking. You should include a visual representation, implications for health as well as noting the constraints of the test. If students are struggling with preparing the report suggest some of the following:

Create a bar graph to compare the three samples on all 7 levels of water quality that they have tested.
Discuss whether they were surprised by any of the results? Why or why not?
They only tested for a few of numerous possible water contaminants; what could be other causes of water contamination?
What are some other possible ways to determine that the water is contaminated without using the water quality test strips?

Homework
None

Embedded Assessment

Students demonstrate their ability to analyze water quality data to determine if water is safe to drink in a written report. Safe laboratory practices can also be assessed.