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Particle Contamination in Bethlehem
Drinking, Tap, and Groundwater
Samples
INTRODUCTION
Background
Water is the basis of all life on Earth, and proper access to drinking water is
essential for our survival every day. However, not all water is of the same quality; the
presence of dissolved particles such as lead and contamination with disease-causing
pathogens have severe detrimental effects on human health. While this problem
primarily affects developing countries, the Flint water crisis has raised awareness of the
often substandard quality of municipal tap water. According to the EPA’s National Public
Water Systems Compliance Report, in 2022, 27% percent of public water systems
“were reported to have violated at least one drinking water standard”. (EPA, 2024).
Thus, there is a need to assess the effectiveness of public water systems in reducing
particle contamination relative to portable water filtration systems and water collected
directly from the ground.
This experiment will use light microscopy to discern and compare particle
contamination in four water samples from Bethlehem, Pennsylvania: one ground-water
sample obtained from melted snow on the sidewalk, two tap water samples from
different locations (the Hitch residence hall and the STEPS building) on the Lehigh
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University campus, and one filtered water sample from a ZeroWater filter dispenser. We
will then centrifuge the samples and examine the pellets under the microscope to further
observe differences in samples with lower particle concentrations. Thus, our main focus
in this experiment was elucidating the differences in particle content between
ground-water, tap water, and filtered water.
Objective
The objective of this experiment is to determine the differences in particle
presence in samples of ground-water, tap water from different locations, and filtered
water under a light microscope. To account for the possibility of lower particle
concentrations, we will additionally view the pellet of centrifuged samples of each water
type to examine more subtle differences in particle content.
Research Questions
●​ What are the differences in particle content between ground-water, tap water,
and filtered water?
●​ Does tap water collected from different locations on the Lehigh campus differ in
particle presence?
Hypothesis
Ground-water will have the greatest particle concentration when viewed under a
light microscope, followed by tap water, with filtered water having the least at little to no
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particles found. There is little difference in tap water particle content by location of
sampling.
METHODS
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First, we obtained large samples (an average size of approximately 5 fluid
ounces) each of ground-water, tap water from 2 different locations, and filtered water
from the Lehigh. The ground-water sample (G) was collected from partially melted ice
on the side of the road into a cup, while the first tap water sample (T1) was taken from a
Hitch residence hall bathroom tap in a small plastic bag. The second tap water sample
(T2) was gathered in a test tube from a tap in a 4th-floor STEPS building laboratory
facility. The filtered water sample (F) was collected from a tap water-fed ZeroWater
32-Cup Ready Read Filter Dispenser model ZD-032-RR in a small plastic bag.
Approximately 20 microliters of each sample were then transferred onto four
slides using a micropipette, before coverslips were added onto the samples. The
samples were then viewed using a light microscope under first a 10X and then focused
on a 40X objective, with pictures (40X) and data noted on any particles found.
Then, we pipetted 50 milliliters (50,0000 microliters) of each sample into labeled
test tubes and centrifuged them. After centrifuging, we pipetted about 20 microliters of
the pellet (if there was no visible pellet formation, from the bottom of the test tubes) onto
four additional slides, covered them with coverslips, and observed them with a light
microscope under 10X and 40X (pictured and used for data) objectives.
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Results
Table 1: Uncentrifuged Samples Under Light Microscope (40X)
Sample
Image Under 40x
Description
F
Clear for the most part, except for a
moderately sized, somewhat twisted
grey smear. The smear is not an
obvious particle, though its presence is
notable. It may be some kind of fiber.
T1
The water is mostly clear, except for a
large, possibly biological grey mass.
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T2
Pictured is a medium-sized brown,
fibrous mass up against a bubble, with
the rest being clear water.
Ground
There are many small masses (at least
12 large enough to be certain, with the
possibility of other smaller particles) of
primarily brown color, although some
are black, grey, or have greenish parts.
Some, particularly the green ones, may
be biological.
The filtered water was the clearest, with the only distinguishable form being an indistinct
medium-sized grey smudge, possibly fibrous, smaller than each of the particles
observed in the tap water samples. The tap water samples were also predominantly
clear water, with clear particles of large to medium size observed. The ground-water
was the least clear, with the presence of at least 12 small particles counted in only a
single image.
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Table 1: Pellet of Centrifuged Samples Under Light Microscope (40X)
Sample #
Image Under 40x
Description
Filter (F)
Predominantly clear, except for 2
extremely small dot-like particles
(one dark grey, the other smaller
and a lighter grey) and another
very small, indistinct light grey blur
that may be another possible
particle.
Tap Water
1 (T1)
Very clear, except for one small,
solid-looking red mass, the identity
of which is unclear, and a small
grey smudge at the top.
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Tap Water
2 (T2)
Mostly clear, except for one grey
medium-sized fibrous mass as
well as two other small fibrous
masses of the same color.
Ground
(G)
Very high density of particle,
mostly small, of brown, grey, and
green coloring.
Going by the number of distinct particle masses observed per image, particle
concentration was higher in each of the centrifuged pellet samples than in the
uncentrifuged. The total particle volume as viewed was higher in both tap water
samples than the filtered, since the filtered water only possessed 2-3 particles of
miniscule size while the total size of the tap water particles were estimated to be many
times that. The combined size and concentration of the particles in the ground water
pellet sample outshot all the other samples by a wide margin.
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DISCUSSION
In both sets of samples, both centrifuged and uncentrifuged, the filtered water
contained smaller particles and lower total particle volume than each of the two tap
water samples, which in turn had a lower concentration and total particle volume than
the ground water samples. This suggests that Bethlehem’s municipal water filtration is
mostly effective at reducing particle concentration and volume from sources such as
ground water, although some particles were still found in tap water.
The results also appear to show that filtration of tap water has success in
reducing the net particle mass, especially in removing larger particles. Interestingly, the
images of the filtered water had similar concentrations of particles observed as the tap
water; however, this does not necessarily mean that filtering was not successful in
reducing particle concentrations. As the experiment was limited to searching for areas
with recognizable particle particles rather than counting over randomly sampled areas,
there is a bias towards areas with high concentrations of particles. In addition, as the
samples were scanned visually to find the presence of particles, there may be a bias
toward finding larger, more immediately recognizable particles as observed in the tap
water images. This also explains the discrepancy in particle size, as larger particles on
average were found in the tap water and uncentrifuged filtered water samples than the
ground water samples. Given that the high particle density of the ground water samples
did not necessitate any additional searching for areas with particles to view, there was
no bias in the images towards larger particles.
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Techniques to prevent these biases and provide more accurate data on particle
size and concentration for future experiments include Coulter Counters, nanopore
sensors, light obscuration, and various microfluidics-based technologies. (Zhang, 2009;
Demeule, 2010)
According to the results of this experiment, there was no consistent, noticeable
difference between the particle volume and concentration of samples T1 and T2. This
suggests that differing locations in the same public water system may have little effect
on the water quality. However, given that both locations of sample collection were both
newer buildings as well as both located on Lehigh University’s Asa Packer campus and
in the same area of the City of Bethlehem, this may not account for larger distances and
differences in location. In fact, research suggests that pipe age may account for
differences in metal ion and microbial content in tap water within the same public water
system. (Su, 2022)
In all of the samples, those from the water in the centrifuged test tubes had
greater particle concentrations. Particle size and total particle volume as assessed
visually had less consistent differences, except for in the ground water samples (the
only one to produce a visible pellet) where there was a large difference in total particle
volume. However, this lack of an increase in particle content in the tap and filtered
samples may be accounted for by random chance of the uncentrifuged samples
possessing larger particles as well as the uncertainty of how much of the samples truly
originated from the pellets, since all the samples except for the ground water did not
have visible pellets.
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This experiment provides evidence of the limitations of municipal water filtration,
including the presence of large particles in tap water, as well as the potential of further
personal filtration for reducing this particle content. However, the use of light microscopy
and visual observation are important constraints on the data. Further research is
needed to confirm these results.
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REFERENCES
1.​ Environmental Protection Agency. (2024, December 5). Providing Safe Drinking
Water in America: National Public Water Systems Compliance Report. EPA.
https://www.epa.gov/compliance/providing-safe-drinking-water-america-nationalpublic-water-systems-compliance-report
2.​ Zhang, H., Chon, C. H., Pan, X., & Li, D. (2009). Methods for counting particles in
microfluidic applications. Microfluidics and Nanofluidics, 7(6).
https://doi.org/10.1007/s10404-009-0493-7
3.​ Demeule, B., Messick, S., Shire, S. J., & Liu, J. (2010). Characterization of
particles in protein solutions: Reaching the limits of current technologies. The
AAPS Journal, 12(4), 708–715. https://doi.org/10.1208/s12248-010-9233-x
4.​ Su, Z., Liu, T., Men, Y., Li, S., Graham, N., & Yu, W. (2022). Understanding
point-of-use tap water quality: From instrument measurement to intelligent
analysis using sample filtration. Water Research, 225, 119205.
https://doi.org/10.1016/j.watres.2022.119205