WHAT’S IN YOUR WATER? PreviousNext We take for granted the water we use to brush our teeth, wash our clothes and keep our lawns green. However, water is an extremely limited resource on the planet and we need to conserve and protect it from pollution. Today you will learn how the levels of chemicals (natural and added) are measured in different sources of water and learn whether they are a danger to your health. LEARNING OBJECTIVES In this laboratory you will learn: · To identify what factors can contribute to water quality · To use negative and positive controls to validate experimental results · To use laboratory techniques to test for the presence of chemicals/molecules in our water · To find other resources of information on water quality ACTIVITIES What you will do in lab today- · Each pair of students will choose a sample of water to test · Each pair of students will perform assays on their water sample to determine whether it contains iron, chlorine, ammonia, calcium or magnesium, nitrates and oxygen · Each pair will report their results on their water sample ASSESSMENTS · Lab report (75): This is your first lab report of the semester –  make sure you read the resources on writing a lab report and use the rubric – you can link to those here. INTRODUCTION PreviousNext Water is a chemical (H2O) that all life depends on. It makes up about 60% of the human body and our cells and organ systems are dependent on its unique characteristics. It is an important solvent, which means that many things dissolve into it (see below for a short list). For example, table salt easily dissolves in water. Also, water naturally has a pH of 7, but when other chemicals are present the pH can change. When pH decreases, we call that acidic. As human population grow, so do their needs for, including their need for water. Many researchers believe that in the next 20 years over half the world’s population will have a shortage of potable or drinkable water. Despite the fact that 75% of the surface of earth is covered in water, 97% is salt water in the oceans and another 2% is frozen in glaciers, leaving us with less than 1% to use. Scientists hope to develop methods to increase potable water using desalination techniques, but in the meantime we have to take care not to contaminate or pollute our current drinkable water sources. Toxins in the water are absorbed or consumed by primary producers and primary consumers – those “low”on the food chain – like bacteria, algae, protists and invertebrates. As toxins are transferred “up the food chain” or from one trophic level to the next, they are concentrated and become even more toxic to the organism. This phenomenon is called bioaccumulation or biologic magnification (Figure 1). This is one reason that humans need to be concerned about pollution in natural rivers and lakes in addition to our public drinking water. Figure 1. Bioaccumulation or biomagnification. The accumulation of a chemical (in this case the + s.

1. WHAT’S IN YOUR WATER?
PreviousNext
We take for granted the water we use to brush our teeth, wash
our clothes and keep our lawns green. However, water is an
extremely limited resource on the planet and we need to
conserve and protect it from pollution. Today you will learn
how the levels of chemicals (natural and added) are measured in
different sources of water and learn whether they are a danger
to your health.
LEARNING OBJECTIVES
In this laboratory you will learn:
· To identify what factors can contribute to water quality
· To use negative and positive controls to validate experimental
results
· To use laboratory techniques to test for the presence of
chemicals/molecules in our water
· To find other resources of information on water quality
ACTIVITIES
What you will do in lab today-
· Each pair of students will choose a sample of water to test
· Each pair of students will perform assays on their water
sample to determine whether it contains iron, chlorine,
ammonia, calcium or magnesium, nitrates and oxygen
· Each pair will report their results on their water sample
ASSESSMENTS
· Lab report (75): This is your first lab report of the semester –
make sure you read the resources on writing a lab report and
use the rubric – you can link to those here.

2. INTRODUCTION
PreviousNext
Water is a chemical (H2O) that all life depends on. It makes up
about 60% of the human body and our cells and organ systems
are dependent on its unique characteristics. It is an
important solvent, which means that many things dissolve into
it (see below for a short list). For example, table salt easily
dissolves in water. Also, water naturally has a pH of 7, but
when other chemicals are present the pH can change. When pH
decreases, we call that acidic.
As human population grow, so do their needs for, including
their need for water. Many researchers believe that in the next
20 years over half the world’s population will have a shortage
of potable or drinkable water. Despite the fact that 75% of the
surface of earth is covered in water, 97% is salt water in the
oceans and another 2% is frozen in glaciers, leaving us with less
than 1% to use. Scientists hope to develop methods to increase
potable water using desalination techniques, but in the
meantime we have to take care not to contaminate or pollute our
current drinkable water sources.
Toxins in the water are absorbed or consumed by primary
producers and primary consumers – those “low”on the food
chain – like bacteria, algae, protists and invertebrates. As toxins
are transferred “up the food chain” or from one trophic level to
the next, they are concentrated and become even more toxic to
the organism. This phenomenon is
called bioaccumulation or biologic magnification (Figure 1).
This is one reason that humans need to be concerned about
pollution in natural rivers and lakes in addition to our public
drinking water.
Figure 1. Bioaccumulation or biomagnification. The
accumulation of a chemical (in this case the + signs)

3. accumulates as the trophic level increases from I to IV.
There can be tremendous variation from one water sample to the
next. Here are some chemicals that can dissolve in water and
how they affect its quality. Keep in mind that just because a
chemical or ion is present, does not mean the water is dirty or
non-potable.
1. Iron (Fe): This element can sometimes be found at high
levels in well water because the iron in rocks dissolves into
rainwater as it seeps deep into the earth. Iron is not unhealthy,
but high levels can discolor the water making it appear reddish-
brown – high iron can discolor food that is cooked in this
water.
2. Chlorine (Cl): This is a powerful oxidizing chemical used to
kill microorganisms in our drinking water, making it safer to
drink. However, this means that significant levels of chlorine
are found in most waterways.
3. Ammonia (NH4): Ammonia is used in fertilizer, animal feed
production, and certain kinds of manufacturing. This chemical
is very toxic and the human body will immediately convert it to
urea for excretion. Simpler animals such as fish just release
ammonia into the water where it becomes diluted. But in fish
tanks with unchanged water, it can accumulate and kill the fish.
High levels can turn up in our water supplies. It can also be an
indication of fecal contamination.
4. Calcium and Magnesium (Ca and Mg): These presence of
these minerals are what determine the “hardness” or “softness”
of water. Low concentrations of calcium or magnesium are soft
– high concentrations make the water hard. Soft water requires
less soap to produce lather and generally has a lower pH, which
can become corrosive if too acidic. Water around DC is hard
and this can cause a build-up of calcium deposits in pipes and in
bathtubs.
5. pH: This is the measure of how acidic or basic water can be.
pH 7 is the neutral pH that is optimal for most living organisms.
Low pH indicates acidic conditions. You may have heard
about acid rain in the news. Plants and animals are sensitive to

4. acid rain, as well as water that is very basic and has a high pH.
6. Nitrates and Nitrites: Living organisms require a source of
nitrogen and they must have it in the form of nitrate. Nitrates
are found in fertilizers and can accumulate, especially in water.
Nitrates are a primary water pollutant because when it rains, the
nitrates are washed out of yards, farms and fields into rivers,
lakes, streams, and eventually the oceans. If there are high
levels of nitrates in the water, algae will overgrow and use up
all the oxygen, which depletes oxygen from fish and larger
animals.
7. Oxygen (O): Living organisms including those that live in
water require oxygen. Oxygen can dissolve in water at different
concentrations depending on temperature and the presence of
photosynthesizing organisms. There are currently large areas of
the Chesapeake Bay that are oxygen-depleted as a result of
pollution from nitrates and phosphates. Nothing can survive in
these waters.
As you can see from the list above, water can vary
dramatically from one source to the next. In addition to
chemicals, living organisms can also be in drinking water. For
example, bacteria are everywhere in our environment but most
are not pathogenic (harmful). One class of bacteria that is
considered a problem if it gets into our water systems is
the Enterobacteria. This group includes E. coli, which can cause
disease. Clean drinking water is treated and clear of these
particular types of bacteria.
For more on the properties of water visit the corresponding
chapter in the Concepts of Biology text:
· Concepts of Biology – Water
For more information about water quality and testing visit this
website.
· https://water.usgs.gov/edu/waterquality.html
To learn more about the Environmental Protection Agency and
their policies on water quality in our area visit this website.
· https://www.epa.gov/standards-water-body-health/what-are-
water-quality-standards

5. BASIC METHODS & EXPERIMENTS
PreviousNext
The class will be divided into groups and each will analyze a
water sample – groups will test the same water sample in a
series of assays. First, make observations of the water sample,
including its appearance and odor. Record these observations in
your lab notebook! Based on these observations and what you
know about the source of the water, make a hypothesis and
prediction about the characteristics and/or quality of this water
sample. Then each group will perform the assays on their water
sample and record the results in their notebook.
Stations are set up for each test with positive and negative
control solutions for:
1. iron
2. ammonia
3. magnesium/calcium
4. chlorine
Positive and negative controls are samples that are tested
alongside your water sample – the scientist selects these
because he/she knows that they contain or do not contain the
substance being tested for. The positive control has the
substance being tested and the negative control does not. You
must compare the results for your sample with the positive and
negative controls at each station to determine if that substance
is present in your water sample. This means you will set
up three tubes at each station: 1) your water sample, 2) a
positive control and 3) a negative control. The reagents and
directions for each test will be organized at stations around the
room.
In addition to these qualitative assays that you will perform,

6. you will:
1. examine the bacterial content of your water sample
2. determine the amount of dissolved oxygen in your water
sample
3. determine the pH of your water sample
4. determine the level of nitrates in your water sample
5. determine whether D.C. water tests positive for lead
DETAILED PROTOCOLS & PROCEDURES
PreviousNextPROCEDURE
Start by adding 0.5 mls of your water sample to
6 microcentrifuge tubes. Label the tubes for each of the
tests.STATION TESTING FOR IRON
Positive Control = Ferrous Chloride; Negative Control =
Distilled Water
1. Using a clean pipet,add 5 drops of sulfuric acid to each
samplein the microcentrifuge tubes. Close the lid and shake
well.
2. Using the scoop provided,place a very small scoop of
ammonium thiocyanate crystals into the microcentrifuge tubes.
Close the lid on the tube and shake well
3. The formation of an orange or dark purple solution is a
positive indicator for the presence of iron.
4. Record your results for this test in the appropriate space in
Table 1. writing either (+) to indicate the presence of iron or (-)
to indicate the absence of iron.
Station Testing for Chlorine
Positive Control = 1% Chlorine Bleach; Negative Control =
Distilled Water

7. 1. Using a clean pipet,add 3 drops of O-Tolidineto the
samplesin the microcentrifuge tubes. Close the lid on the tube
and shake well.
2. The formation of a reddish-brown color is a positive indicator
for the presence of chloride. Light tan or yellow is negative.
3. Record your results for this test in the appropriate space in
Table 1. writing either (+) to indicate the presence of
chlorine or (-) to indicate the absence of chlorine.
Station Testing for Ammonia
Positive Control = Ammonium Chloride; Negative Control =
Distilled Water
1. Pipette 0.5mL of your water sample into a microfuge tube.
2. Add 2 drops of Ammonia Test
Solution
#1.
3. Add 2 drops of Ammonia