IS BOTTLED WATER BETTER THAN TAP WATER?
Camilla Hurst and Kaylen McCluskey
S3ENa, Luxembourg 1
Monitor: Mr. Mallon
Abstract
More and more bottled water is being consumed, creating waste from plastic bottles. Tap
water comes from local reservoirs and wells, while bottled water is transported long
distances consuming energy and producing CO2. Recently, some supermarkets have sold tap
water in plastic bottles. This raised the question: is bottled water better than tap water, or
is it just marketing?
The hardness of water is an important factor in in determining taste, therefore we tested
the hardness of bottled water and tap water at the school. The hardness depends upon the
calcium and magnesium content, which we measured with EDTA chelation. Tests for other
minerals and a microbiological analysis were performed with the help of the Administration
de la gestion de l’eau, Luxembourg. The microbiological analysis was done for samples from
different locations, before and after sterilisation of the outlet/taps. We found our samples
to be good quality. However, we found some bacterial contamination of water from the
school’s drinking fountain and rust in one outlet. We conclude that tap water is of equal
quality to bottled water, but to maintain its quality taps must be kept clean and pipes well
maintained.
We also carried out blind taste tests of three samples (tap water, and two mineral waters).
Half of the approximately 80 students preferred the sample of intermediate hardness
(bottled) with the rest split between tap water and a high mineral content water.
Our recommendation is: fill your bottle at a clean tap!
1. Introduction
Our aim was is to determine whether Luxembourgish tap water has the same quality
as that of bottled water. We were motivated to carry out these experiments because
we read that tap water was being sold in bottles as “mineral water” by some
supermarkets. This could mean that bottled water is actually nothing more than
marketing.
Bottled water causes environmental problems because of the plastic bottles it is sold
in. Bottled water is also transported through long distances using energy and
producing CO2. Let’s take the example of San Pellegrino, a bottled water that is
common in Luxembourg. It must travel 700km from the source in Italy to our shops
as shown in the map.
So we wanted to test the quality of water in terms of:
•
•
•
chemical content
biological purity
taste
To do this experiment we worked with the Administration de la gestion de l’eau,
Luxembourg.
2. Water in Luxembourg
In Luxembourg tap water comes from a reservoir in the north of the country (the
lake of Esch-sur-Sûre) or a fractured rock aquifer made up from Luxembourg
sandstone. In many regions this water is blended. However, the source of the tap
water going to our school is the reservoir.
The chemical content of water depends upon the rocks in which it is in contact with.
It can also be contaminated by pollution from fertilizers and pesticides. However, it
is treated to bring it in line with European water standards.
3. Experiments for water hardness
The hardness of the water is an important factor in influencing the taste.
(http://chemwiki.ucdavis.edu/Inorganic_Chemistry/Descriptive_Chemistry/Main_Gr
oup_Elements/Main_Group_Reactions/Case_Study%3A_Hard_Water).
Hard water is water containing high amounts of mineral ions. The most common
ions found in hard water are Calcium (Ca2+) and Magnesium (Mg2+). These ions can
precipitate out leaving calcination on taps and equipment. Hard water may also
react with other substances in the solution, such as soap, to form "scum."
Hard water has many health benefits when compared to soft water. Both calcium
and magnesium are considered essential nutrients, meaning that they must be
provided in the diet in order to maintain healthy body function. Calcium is a critical
component of bones, and has many positive effects on the body, such as prevention
of serious life-threatening and painful ailments like osteoporosis, kidney stones,
hypertension, stroke, obesity, and coronary artery disease. Magnesium also has
positive health effects. Inadequate amounts of magnesium in the body increase the
risks for some forms of health problems, such as hypertension, coronary heart
disease, and diabetes. Studies done on the health effects of hard and soft water
have shown that people who drink greater amounts of soft water have much higher
incidences of heart disease, as well as higher blood pressure and cholesterol levels,
and faster heart rates than those who drink mostly hard water. Furthermore, soft
water is corrosive to pipes, which may allow for toxic substances like lead to
contaminate drinking water.
Therefore, we started our research by examining the hardness of water sample
taken from the school tap and from a Luxembourg bottled water, Cristaline.
Our school water samples came from the school inlet and a drinking fountain. We
were expecting the hardness to be very similar, although we thought it would be
interesting to have a comparison of two different locations.
To conduct this experiment we used a solution called EDTA
(Ethylenediaminetetraacetic acid) which is a chelating agent. This means that it binds
with Calcium and Magnesium ions.
http://homepages.ius.edu/DSPURLOC/c121/week13.htm
The experiment is to drip EDTA into a 50cm3 water sample into a test tube
containing an indicator (NET). The indicator changes colour, from purple to blue,
once all the Calcium and Magnesium had bound to the EDTA. We were able to
obtain an accurate amount of EDTA for this because the colour change occurs with
one drop.
Our initial quantity of EDTA was 50ml held in a test tube above our sample. This
EDTA had a concentration or molar value of 0.01. As we have mentioned, the EDTA
was released drop by drop. With the Cristaline sample, 14.05 cm3 of EDTA was
added before the indicator changed colour.
The moles of EDTA added is given by the formula below, which also indicates the
number of moles of calcium and magnesium ions.
Moles =
=
0.01 ( 𝐸𝐷𝑇𝐴 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛)𝑋 𝑣𝑜𝑙𝑢𝑚𝑒 𝑎𝑑𝑑𝑒𝑑
0.01 𝑋 14.05
1000
1000
= 1.405 𝑋 10-4
The sample volume = 50cm3 = 0.05L
Moles/litre=
1.405 𝑋 10−4
0.05
=2.81 X 10-3
To convert from moles to grams you need to multiply by the formula mass (CaCO3
for total hardness). Formula mass is calculated from adding up atomic masses,
found in the Periodic Table. CaCO3 formula mass = 100.1
Therefore, (2.81 x 10-3) x 100.1 = 0.281281
To convert ppm to mg/l you need to multiply by 1000
0.281281 x 1000= 281.281
Total hardness= 281.281 ppm
With the water sample from the school drinking fountain, the indicator changed
colour with 3.90 cm3 of EDTA. Repeating the calculation
Moles =
0.01 𝑋 3.9
1000
= 3.9 𝑋 10-5
Sample volume= 50cm 3 = 0.05l
Moles/litre =
3.9 𝑋 10−5
0.05
=7.8 X 10-4
(7.8 x 10-4) x 100.1 = 0.078078
To convert ppm to mg/l you need to multiply by 1000
0.078078 x 1000 = 78.078 ppm
Total hardness = 78.078 ppm
And with the sample from the inlet, 3.975 cm3 of EDTA was required which gives a
hardness of 79.58 ppm
As expected the hardness of the inlet water and that of the drinking fountain is the
same. The results are shown in the figure below.
Tested Hardness
300
250
200
150
100
50
0
Cristaline
Drinking
fountain
Inlet
Our conclusion is that bottled water is harder than Luxembourgish tap water. This is
because tap water is from a reservoir which has had much less contact with calcium
and magnesium containing rocks. This means that bottled water might have some
beneficial health effects, though it depends upon the source of local tap water.
4. Experiments for biological contamination
Bacterial contamination cannot be detected by taste, smell or sight. Floods, human
or animal waste, or insects, rodents or animals entering a well can be a cause for
bacteria.
Many strains of bacteria are not toxic but even mild cases can cause minor illnesses
like diarrhea, vomiting, cramps, and other gastrointestinal symptoms.
A particular problem is E.Coli. This stands for Escherichia Coliform bacteria which
normally live in the intestines of humans and animals. Most strains of this bacteria
are harmless, but one particular strain called O157 can cause severe kidney damage
and diarrhea and even kidney failure and death.
Because E.Coli are always present in human and animal faeces in high numbers, they
are used as an indicator of pollution in drinking water. When E.Coli are detected this
does not mean that O157 is present but it requires immediate action. These
bacteria can be rapidly removed by chlorine and other disinfectants used in the
treatment of water supplies. Outbreaks of illnesses are mostly related to poor
maintenance of disinfection systems.
We started our microbiological analysis with a Coliert-18 test kit (produced by IDEXX
laboratories, USA) to measure the presence of E.Coli and coliform bacteria in our
water sample.
Coliform bacteria (present in faeces) were tested because while coliforms
themselves are not normally causes of serious illness, they are easy to culture and
their presence is used to indicate that other pathogenic organisms of faecal origin
may be present.
The test involves pouring our 100ml sample of water from the school inlet onto a
tray with fifty wells (a “Quanti-Tray”). The tray was then sealed and placed in an
incubator at 35°C for 18 hours. The cells turn yellow when E.Coli or coliforms
bacteria are present.
Fortunately, our sample was transparent. This means that our sample was negative
for E.Coli and coliforms.
Our sample is the one on the left. The sample on the right is one with E.Coli so that
we could examine the difference.
We did an additional test of E.Coli and coliforms with a sample from the school
drinking fountain with a test purchased from Simplex Health (www.
Simplexhealth.co.uk). This test was also negative.
For a number of other tests we took 9 samples of tap water from around our school
for our microbiological analysis. For 5 of these samples, we sterilized the tap so that
the germs on the tap itself wouldn’t affect the water. We also wanted a comparison
of samples taken at the same location to determine whether the cleanliness of our
school had a (significant) effect on the quality of our tap water, so we took another 4
samples without disinfecting the tap, to try and replicate what the students would
drink.
Our five locations where we sampled our water were: a classroom, a drinking
fountain in the gym, a tap in the toilets, a drinking fountain in the canteen, and the
school inlet (where we didn’t take an unsterilized sample because there is no access
for students so they wouldn’t be able drink from there).
We also tested the presence of intestinal enterococci. To do this 100ml of our
sample was filtered through a membrane of 0.45𝜇𝑚 in order to capture the
enterococci. The resulting residue was placed into a Petri-dish and incubated for 48
hours at 36°C. The results were that our sample had no Intestinal enterococci.
As both E.Coli and intestinal enterococci are indicators of faecal pollution, our results
prove that there are no harmful organisms present in our school water.
We also carried out a detection and enumeration of the total colony count of all
bacteria present.
For the total colony count, we placed 1ml of our samples on agar Petri-dishes. The
samples are them incubated at both 22°C for 72 hours and 36°C for 48 hours.
Testing the samples at these two temperatures are very important because they
represent the bacteria present in the environment (22°C, room temperature) and
bacteria present in humans (36°C, body temperature).
In the agar the colonies are visible as small dots, and counting is done by hand. The
picture below shows the image of one of our samples seen through a microscope
with each colony as a spec.
In the images below we can see our drinking fountain samples. On the top, the
samples are sterile and on the bottom they are unsterile. On the left the samples
are incubated at 36°C, on the right they are incubated at 22°C.
This table shows us our results of the total colony count for all the samples.
Sample
Inlet
Gym unsterilised
Gym sterilised
Classroon unsterilised
Classroom sterilised
Toilet unsterilised
Toilet sterilised
Fountain unsterilised
Fountain sterilised
Bottled
Germs at 22 degrees
(72 hours incubation)
Colony forming units per ml
<1
2
64
101
5
<1
15
>300
90
>300
The results are also shown in the graph below.
Germs at 36 degrees
(48 hours incubation)
Colony forming units per ml
<1
<1
<1
2
<1
>300
2
>300
116
<1
Colony Forming Units per ml of water
300
250
200
150
100
50
0
Germs at 22 degrees (72
hours incubation)
Germs at 36 degrees (48
hours incubation)
One interesting result is the number of germs on the unsterilized taps and drinking
fountains in the school. This indicates the need for good hygiene and regular
cleaning of equipment.
5. Other experiments performed by the Adminstration de la gestion de l’eau
In addition to Calcium and magnesium, water can contain a number of other
chemicals. For example:
a) Nitrates and nitrites
When animal and human wastes or soil fertilisers come into contact with water,
they show up as nitrates and nitrites. These fertilisers are very easily washed off
the land into streams and rivers and can eventually end up in drinking water
supplies. Only specialised water treatment processes can reduce the amount of
nitrate in drinking water. Nitrates and nitrites are especially harmful for the
development of young children and can be a cause of the potentially fatal Blue
Baby Syndrome.
b) Acidity
The pH of tap water should be in the range of 6.5 to 9.5, which is around neutral
and close to alkaline. Some water sources are acidic. Acidic water can be
corrosive to metals in piping and equipment. It is important to control the pH of
water as a too high or too low pH can be an indicator of other problems in the
water.
c) Sulphates
Sulphates are naturally found in most waters. High sulphates will usually
correspond to high sodium levels and high acidity in water. Low to moderate
concentrations of sulphate may actually make water more palatable and
desirable to drink. High levels of sulphates will produce a medicinal taste and can
cause a laxative effect on the digestive system.
d) Chloride
Chloride is found in most natural waters and the concentration depends on the
mineral content of the earth through which the water flows. Naturally occurring
high levels of chloride generally means hard water because of chloride's ability to
combine with calcium and magnesium. Low to moderate concentrations of
chloride may actually make water more palatable and desirable to drink.
Chlorides contribute to the total mineral content of water. Chloride will produce
a salty taste in water and in high concentrations, it will produce a brackish or
briny taste which is undesirable.
The results of the tests of the Administration de la gestion de l’eau are shown in
the table and the graph below.
Results of the chemical analysis for each water sample
pH
NH4
Nitrites
Nitrates
Chlorures
Sulfates
Calcium
Magnesium
Potassium
Sodium
School inlet
water
8
0
0
36
20
33
28
38
4.7
3.2
Bottled water
7.5
0
0
5
5
49
107
4
2
3.5
Comparison of school water and bottled water
120
100
80
60
School inlet water
40
Bottled water
20
0
To note is the higher level of nitrates in tap water as this water is coming from a
reservoir where contamination by agriculture is more likely than for groundwater.
However, the tap water is well within the necessary standards for good quality
water.
Tap water might also be contaminated from pipes. If water is soft or corrosive it can
accelerate the leaching of metals from plumbing. This used to be a problem when
there were lead pipes as lead is very poisonous. Today, pipes are copper or iron.
These metals do not have the same health effects, but they can give an unpleasant
taste. When taking the water sample at the school inlet we noticed rust on the
fitting and this contaminated this water sample. The resulting turbidity is shown in
the chart.
Turbidity
35
30
25
20
15
10
5
0
School inlet water
Bottled water
We also tested the iron content of water from the drinking fountain with a test from
Simplex Health. The result was that the water had zero iron content. This means
that the rust was a local problem due to the tap at the inlet and any rust particles
had deposited out from the water. However, this illustrates the need for wellmaintained and clean taps.
6. Taste tests
Tap water has got the same quality as bottle water. Once we knew this, we asked
ourselves the question whether the students could taste a difference between
different waters, to explain the number of people consuming bottled water in our
school.
To answer our question we carried out blind taste tests on 76 students.
We also prepared a questionnaire on general knowledge on tap water to determine
how much people really knew on water. You can find a copy of this in the annex.
The distribution of water consumption in our sample rages from 1 glass per day to
13 glasses per day as shown in this chart.
Number of students
Number of glasses of water
drunk per day
15
10
5
0
1
2
3
4
5 6 7 8 9 10 11 12 13
Number of glasses
In the questions before the taste test, students claim that there is a difference
between tap water and bottle water and that bottled water is better.
The blind taste test involved the students tasting three types of water – tap water, a
local mineral water and a mineral water with very high magnesium content.
The local bottled water was Cristaline, the same water used in our earlier tests. The
high magnesium content water was Hépar. This has 119 mg/l of Magnesium, which
is 114.8mg/l more than the magnesium content of Cristaline.
The results of our survey is that one-half of students preferred Cristalline, with the
remaining half of the students split equally between tap water and Hépar. This is
shown in the chart below. The preferred water is the one of intermediate hardness.
However, a significant share of students actually prefer tap water.
Which is the tastiest?
tap water
Hépar
Cristaline
One half of the students correctly identified tap water, but the other half were
unable to detect the water type. The pie chart below demonstrates these figures.
Amount of people identifing the
tap water.
tap water
Hépar
Cristaline
Most people think that bottled water costs 10 times that of tap water. One third
think that bottled water costs equal, less than tap water, or is too cheap to care
about. Only 5 percent think that bottled water costs more than 100 times tap water.
In fact, a 0.5l bottle of Cristaline costs €0.90 in the school canteen. The Ville de
Luxembourg quotes an average rate of tap water of 300 litres per euro. Therefore,
the cost of Cristaline per litre of €1.80 compares with €0.03 for tap water. The
bottled water is 540 times as expensive as tap water.
The average water consumption in our sample is 5.7 glasses per day. If each glass is
30 cl, this is equal to 1.7 litres per day, or 624 litres per year. For comparison, the
European Food Safety Authority recommends that women should drink about 1.6
litres of fluid and men should drink about 2.0 litres of fluid per day.
624 litres of tap water would cost €2, while the same quantity of bottled water
would cost €1123. This is a number that would surprise many people.
7. Conclusion about water quality
We found our water samples to be good quality. However, we found some bacterial
contamination of water from the school’s drinking fountain and rust in one outlet.
We conclude that tap water is of equal quality to bottled water as long as the taps
are kept clean and pipes are well maintained in order to prevent leaching of metals
into the water.
We can conclude that, in general, many people are unable differentiate types of
water. We saw this in our blind taste tests where one half of the students correctly
identified tap water, but the other half were unable to detect the origin of the
water.
Also, students don’t take into account the money they spend when buying bottled
water. One third of our tested students thought that bottled water costs equal to,
less than tap water, or is too cheap to care about. In fact, they spend more than
€1000 per year, when tap water costs only €2 a year! That’s money going down the
drain!
We think it is very important that people are made aware of these facts as more
bottled water is being consumed, creating waste from plastic bottles.
Some 30 million plastic bottles are used every day in Europe. As much as 86% of
plastic bottles in the US are not recycled, and approximately 1500 bottles end up in
land fill and the sea every second ( www.safebottles.co.nz ).
Tap water comes from local reservoirs and wells, while bottled water is transported
long distances consuming energy and producing CO2. Not only is tap water more
economical, but many people can’t distinguish tap water between bottled water.
Our recommendation is: fill your bottle at a clean tap!
Acknowledgments
We would like to thank the Administration de la gestion de l’eau for taking their time
to carry out tests with our water samples and allowing us to use the apparatus.
Particular thanks are due to Dr. Zwank for his guidance.
We would also like to thank Mr. Mallon for getting us in touch with the
Administration de la gestion de l’eau and making our meetings possible. We also
thank Mr. Bennett for allowing us to use his classes to taste testing his students.
Tap water or bottled water?
ANNEX
Name: ……………………………
Class:……………………………..
1. How many glasses of water do you drink per day?
(include carbonated water, but not prepared drinks or juices)
2. How many glasses do you drink per day of:
-
Tap water (include from the jugs in the canteen)
-
Carbonated/sparkling water
-
Plain bottled water
3. Do you prefer tap water or bottled water?
-
I prefer bottled water
-
I think they are both the same
-
I prefer tap water
Explain why? …………………………………………………………………………………………………
…………………...…………………………………………………………………………………………………
4. Is there a difference in taste or smell? (tick the answer)
If yes, which is better?
Yes…….....
tap water……….
No………..
bottled water………..
5. Do you trust bottled water more than Luxembourgish tap water?
(tick the answer)
Yes………..
No…………
Explain why? …………………………………………………………………………………………………
………………………………………………………………………………………………………………………
6. In your opinion, bottled water costs: (tick the answer)
-
less than tap water………………………
about the same……………………………
10 times more…………………………….
100 times more…………………………..
1000 times more…………………………
water is too cheap to care……………