A Study on the Total Dissolved Solids and Hardness Level of Drinking Mineral Water in Bangladesh

Abstract

Natural water is being processed by the Reverse Osmosis purification system in the different area of Bangladesh for drinking purposes. Most of the water processing company is being filled the 500 mL, 1000 mL, 2000 mL and 5000 mL bottles with this processed water and being sold these widely in the different markets of Bangladesh. But the dissolved minerals in their purified drinking water do not sufficient for human's health. Total Dissolve Solids (TDS) is a parameter that count all dissolved minerals in the water. Calcium (Ca 2+), Magnesium (Mg 2+) and Potassium (K +) are minerals that introduce as a " Beneficial Minerals " for human health. Calcium is an important mineral for bone development, Potassium is needed for muscles and nervous system and Magnesium might help protect against cardiovascular disease. The objective of the study is determined the Total Dissolved Solids (minerals) and the Total Hardness (Ca 2+ & Mg 2+) in selected drinking bottled water. The selected bottled water has been produced by the local branded company in Bangladesh such as Everest, Spa, Sena, Fresh, Mum, Aquafina, Jibon and Pran. Total Dissolved Solids and Total Hardness are measured in total eight number of bottled water samples which had been collected from the local confectionery shop in Dhaka city. Results have shown in the study, dissolved minerals are found very little in drinking water which is quitealarming level. Particularly, Calcium and Magnesium are found very low in Aquafina, Sena and Jibon branded water. It never benefits to human health. Total Dissolved Solids found the very low range is 9.44 mg/L in Aquafina's water which is not only drinkable but also unsafe and dangerous for human body. It's a negative effect on our human health especially malnourished people's health.

Full text

American Journal of Applied Chemistry
2016; 4(5): 164-169
http://www.sciencepublishinggroup.com/j/ajac
doi:10.11648/j.ajac.20160405.11
ISSN: 2330-8753 (Print); ISSN: 2330-8745 (Online)
A Study on Total Dissolved Solids and Hardness Level of
Drinking Mineral Water in Bangladesh
Mohammad Rafiqul Islam1, *, Mohammad Khairul Islam Sarkar1, Tanzina Afrin2,
Shafkat Shamim Rahman3, Rabiul Islam Talukder4, Barun Kanti Howlader5,
Md. Abdul Khaleque1
1Department of Environmental Science, Independent University, Bangladesh (IUB), Dhaka, Bangladesh
2Department of Civil Engineering, Dhaka University of Engineering & Technology (DUET), Dhaka, Bangladesh
3Department of Mathematics & Natural Sciences, BRAC University, Dhaka, Bangladesh
4Departmentof Biochemistry, Primeasia University, Dhaka, Bangladesh
5Department of Quality Control, Everest Drinks and Dairy Products Ltd, Dhaka, Bangladesh
Email address:
sad.safwan@yahoo.com (M. R. Islam)
*Corresponding author
To cite this article:
Mohammad Rafiqul Islam, Mohammad Khairul Islam Sarkar, Tanzina Afrin, Shafkat Shamim Rahman, Rabiul Islam Talukder, Barun Kanti
Howladar, Md. Abdul Khaleque. A Study on Total Dissolved Solids and Hardness Level of Drinking Mineral Water in Bangladesh.American
Journal of Applied Chemistry. Vol. 4, No. 5, 2016, pp. 164-169. doi: 10.11648/j.ajac.20160405.11
Received: July 21, 2016; Accepted: July 29, 2016; Published: August 17, 2016
Abstract: Natural water is being processed by the Reverse Osmosis purification system in the different area of Bangladesh for
drinking purposes. Most of the water processing companies fill the 500 mL, 1000 mL, 2000 mL and 5000 mL bottles with this
processed water and sell widely in the different parts of Bangladesh. However, the dis solve d miner a ls in t heir pur ifie d
dr inki ng wate r a r e n ot suffici e nt for hum an heal th. To tal Di ssol ve Solid s ( T DS) is a par a met er that co u nts all
di ssol ved mine rals in the wa t er. Calcium, magnesium and potassium are minerals that are introduce as a “Beneficial
Minerals” for human health. Calcium is an important mineral for bone development, potassium is needed for muscles and
nervous system and magnesium is helpful protect cardiovascular disease. The o bjec t ive of t he st udy is to exa m ine t he Total
Dissolved Solids (minerals) and the Total Hardness (TH) in selected bottled water samples. The selected samples have been
marketed by the local branded companies in Bangladesh. TDS and TH are measured in total eight of bottled water samples
collected from the local confectionery shops in Dhaka city. The obtained results show that the levels of dissolved minerals in the
drinking water samples are very low, which is quite alarming. Particularly, calcium and magnesium are found in very low amount
in water samples of three companies. It can be assumed that those bottled water do not bring additional benefits to human health.
The TDS of sample of one company was alarming low (9.44 mg/L. It may pose negative effects on human health especially
malnourished people’s health.
Keywords: Drinking Water, Mineral, Dissolved Solid, TDS, BDS, BSTI, WHO
1. Introduction
Dhaka, the capital of Bangladesh is one of the mega cities in
the world with the population of over fifteen million [Figure
1]. [1]. It is one of the rising cities in Bangladesh. The demand
of drinking water is increasing in all cities of Bangladesh. One
cannot think about life without water. Everyone use water in
their daily life for drinking, washing, flashing, bathing and
cooking. In addition, water is widely used in irrigation,
building construction, electricity and steam generating etc.
Different properties of water are important for users though it
is depend on the purposes for which water is used. The
properties of drinking water must suitable for health. The safe
drinking water is also considered to be a pre-requisite for
developing public health and economic growth. Always, every
thirsty people seek the safe and pure mineral containing
drinking water for filling their body demand. In Bangladesh,

165 Mohammad Rafiqul Islam et al.: A Study on Total Dissolved Solids and Hardness Level of Drinking
Mineral Water in Bangladesh
most of peoples are very blessed regarding availability of one
of the most important natural resource, water. But they cannot
use it properly due to contamination of natural resources.
Population growth, global warming, rapid industrialization,
water, lack of adequate and improved management of natural
resources are leading to increased water pollution in an
alarming rate. The standard specification (Table-1) of purified
drinking water has been set by Bangladesh Standard &Testing
Institution (BSTI). The specification’s for natural mineral
water and natural drinking water are respectively
BDS-1414:2000 and BDS-1240:2001 [2].
Figure 1. Map of Dhaka City, Bangladesh.
Total Dissolve Solids (TDS) are measure of the combined
content of all inorganic and organic matters or salts which are
found in water. The main ingredients are usually the cat ions
such as calcium, magnesium and potassium and the anions
such as carbonate bicarbonate, nitrate, chloride sulfate etc.
Among the contents of TDS, dissolved calcium and
magnesium in the water is called “Hardness”. Some ions of
the above mentioned are essential where as some ions are
toxic to human health. Low TDS and TH in water are defined
in this paper as that containing 1-100 mg/L [3]. This is typical
of the water quality obtained from distillation, reverse osmosis
and deionization system of use water treatment. As per the
BDS-1414:2000 and BDS-1240:2001 standards of BSTI, the
maximum TDS level are 1000.00 mg/L and 500.00 mg/L

American Journal of Applied Chemistry 2016; 4(5): 164-169 166
respectively [2]. Along this, the maximum range for hardness
level in drinking water is 300.00 mg/L. Although; a minimum
level of TDS and TH for drinking water are not specifically
mentioned for drinking water is not specifically mentioned in
their standard.
According to the medical science, the lower level of
minerals in water never benefits for thirsty and malnourished
peoples. In Bangladesh, most of the people don’t know the
benefits of dissolved minerals for maintaining their good
health. After 1988 flood when hepatitis broke out widely,
drinking bottled water entered into the local market of
Bangladesh as safe. Since then, the private companies are
producing bottled drinking water (arsenic & cyanide free) by
reverse osmosis purification system. BSTI also have been
issued the license to around 275 manufacturers of which 100
are filling only jar with their purified drinking water [4, 10].
However, they do not maintain the level of beneficial
dissolved minerals properly in their processed water.
Figure 2. Packaging Unit of Mineral Drinking Water.
Most of the bottled drinking water manufacturers are
producing the desalinated, de-mineralized water and selling to
the local market by labeling “Pure Mineral Water”.
The World Health Organization conducted a study that
revealed some health risks associated with drinking water
without dissolved minerals especially hardness (calcium and
magnesium) level. Few of the risk include kidney problems,
gastrointestinal problems, heart disease, pregnancy
complications, bone density issues, joint conditions,
cardiovascular diseases anemia fracture, growth disorders etc.
It has been also reported that the low mineral drinking water
increase the dieresis and the elimination of calcium,
magnesium, sodium, potassium, nitrate and chloride ions from
the body [5].
According to WHO, the range for hardness (calcium &
magnesium) in drinking water is 100-500 mg/L. Two
important components of total hardness are calcium &
magnesium is needed for dietary. They also result in beneficial
effects on bone structure [6]. In addition, mineral shall do the
balance of body ions and energy. The presence of dissolved
solids in water may affect its taste. Generally, the taste of
water containing low mineral is sour or flat .On the other hand,
water containing excess minerals tastes metallic, salty, earthy
etc [3, 7, and 17]. So, significant deviation of TDS level in
water from the standard values is unacceptable to consumers
not only because of taste but also due to other effects.It is
remarked that the possible bacterial contamination in the
lower TDS water which is also very harmful to human
health. All coliform bacteria do not cause for diseases.
However, some rare strains of E. coli, particularly the strain
0157:H7 can cause serious illness [5, 8, 23]. According to
the medical science, calcium, magnesium, potassium are
the beneficial components for bone, teethes and plays an
important role a co-factor than 300 enzymatic reactions in
the body including glycolsis, ATP metabolism, transport of
minerals through membranes, synthesis of proteins and
nucleic acids, neuromuscular excitability and muscle
contraction [3, 5, 6].
The World Health Organization conducted a study that
exposed some health risks associated with drinking water
without minerals. Few of the risks include kidney problems,
gastrointestinal problems, bone density issues and
cardiovascular diseases etc. [3, 5]. The kidneys are most
important constant mineral’s concentration through elimination
and re-absorption. In homeostasis, three body fluid are involved:
Plasma (3/5 of the blood Volume), Interstitial (fluid between
cells), intracellular (fluid inside the cells) [3]. The concentration
of sodium ions is the highest outside the cell and that of
potassium ions is the highest inside the cells. When the osmotic
pressure is high on one side of the cell membrane (higher
concentration of ions/minerals) and lower on the another side
(low concentration of ions/minerals), water moves across the
cell membrane from the dilute side toward another side to
equalize the osmotic pressure. This phenomenon is known
Reverse Osmosis process. The concentration of normal ions or
minerals of all these fluid is about 300 mM/L [3]. Any changes
from normal in ions or minerals concentration across the cell
membrane are corrected in one minute or less because water
moves quickly through cell membranes. Therefore, small
changes in os-molality from drinking water are quickly brought
to equilibrium. The kidneys control the overall concentration of
the constituents of body fluid.
The typical kidneys filter approximately 180 liters of
plasma/day and each of the 3.0 liters of plasma gets filtered
about 60 times [9, 22]. To replace this much water have to
drink a 12- ounce soft drink every 3 minutes of the day
fortunately 99% of the filtrate gets reabsorbed, leaving 1.5-2.0
liters of urine per day [11, 12]. If the os-molality of the fluid to
be filtered by the kidney is lower than normal, nervous and
hormonal feedback mechanisms cause the kidney to excrete
more water than normal. Thus, the mineral’s concentration in
the blood and body fluids are quickly maintained by the
kidney through homeostasis. If homeostasis is not maintained
because of major diet mineral deficiencies, diseases,
consuming lower minerals in drinking water would be minor
causes. (If any) factor in any observed symptoms, It is
apparent that disease, physiological dysfunction, or major
nutritional deficiencies many causes a “leaching” problems,
but not consuming one to two liters of low level of TDS water
on a daily basis.
2. Manufacturing Process
Most of the mineral water industries are manufacturing the
mineral water by using the Reverse Osmosis (RO) system
[Figure 3 & Figure 2] which is a purification technology that

167 Mohammad Rafiqul Islam et al.: A Study on Total Dissolved Solids and Hardness Level of Drinking
Mineral Water in Bangladesh
uses a permeable membrane to remove large healthy and
unhealthy minerals, organic & inorganic molecules, mono &
multivalent ions and some bacteria & viruses from the
untreated water. It is noted that the semi permeable membrane
technology of RO was first observed in1748 by Jean-Antoine
Nollet. By the end of 2001, about 15200 desalination RO
plants were in operation or in the planning stage or worldwide
[13]. The pore size of membrane filter is 0.0001 microns [13,
14] which does not allow the minerals to pass through. After
passing through the RO membrane, the water goes to a post
final filter like as Activated Carbon Filter (ACF). After
removing the remaining odors, tastes, organic chemicals,
chlorine and other suspended solids by the ACF, water goes to
storage tank and fills the bottles with this water. In this
manufacturing system, there is no opportunity to add the
necessary minerals in produced drinking water.
Figure 3. Reverse Osmosis Unite of Mineral Drinking Water.
Due to the lack of accurate monitoring, manufacturers are
producing the desalinated /de-mineralized water and selling to
the market of Bangladesh randomly.
3. Materials and Method
3.1. Sample Collection
Total eight bottles of mineral water (Size: 500 mL) of
different brand were collected from different confectionery
shops in Dhaka city and storage at below 10°C in the
laboratory refrigerator. TDS & TH of the samples were
measured according to the standard methods EPA Method
#160.1, Gravimetric and Dried at 180°C [15] and EPA Method
130.2, Titrimetric, EDTA [16] respectively.
3.2. Apparatus
For the analysis of total solids in different collected
drinking water sample, the following apparatus were used in
the laboratory-
 Filtration Unit, Glassco, UK (Glass Fiber Filter Disk, 2.1
cm, Air Suction Pump (Model Rocker-300),Suction
Flask 500 mL)
 Evaporating dish, 100 ml
 Hot Plate (Model: AREC, Velp, Italy)
 Water Bath (Model:HH.S21.4)
 Drying Oven (Model:3606,Branstead)
 Desiccators
 Graduated cylinder, 100 ml
 Analytical Balance (Model: EW 220-3NM, Kern,
Germany)
 Refrigerator (Model: RR-618MW, Rangs).
3.3. Analytical Procedure
200 mL of each sample was filtered through a standard
filtration unit using glass fiber filter disk, glass beaker,
membrane filter paper, vacuum pump. 100 mL of each filtrate
sample was transferred into evaporating dishes using 100 ml
graduated cylinders. The evaporating dishes were heated at
550°C for an hour in hot plate. The evaporating dishes were
cooled in desiccators and the weight of each dish was measured
immediately.Each filtrate samples which were transferred is
evaporated and dried to constant weight at 180°C in Oven and
cooled in desiccators before taking the weights [15].
The total hardness of water was determined by
complexometric method where Na2-EDTA was used as
complexion agent and Eriochrom Black T was used as an
indicator [16]
3.4. Calculation
To calculate the TDS of each sample the following equation
was used:
TDS (mg/L) = {(A - B) x 1000} ÷ Volume of sample
Where, A = Weight of evaporating dish and dried residue
B = Weight of evaporating dish
4. Results and Discussions
Different government has different regulations for the TDS
level for drinking water. According to the BSTI guidelines, the
maximum level of TDS for mineral bottled water and natural
drinking water are 1000.00mg/L and 500.00 mg/L
respectively [2]. A review was performed of the Bureau of
Indian Standards, United States, Canadian, World Health
Organization (WHO) and European Community (EC) for
drinking water standards. The Bureau of Indian Standards
(IS10500), United States recommended the maximum level of
TDS is 500.00mg/L for drinking water, the Canadian
guidelines suggest less than 1000mg/L, and the EC Maximum
Admissible Concentration (MAC) is 1500.00 mg/L. None of
them has minimum limits or optimum levels of TDS [12, 17,
18, 19]. It can be assumed that according to these guidelines,
TDS level can be even 0.00 mg/L in the drinking water which
does not have any minerals. Water could be transparent, clear,
and drinkable without the presence of minerals. However,
absence of minerals in drinking water will not fulfill the body
demand and there will be no taste. Therefore, necessary
minerals required for having suitable taste and for fulfilling
the lack of minerals for public health. An isolated report, a
summary of Russian studies available through the WHO, has
recommended that human body fluid and electrolytes are
better replaced with water containing a minimum of 100.00
mg/L of TDS [20]. WHO’s team (1980) recommended that an
optimum level of TDS should be about 200.00-500.00 mg/L
for chloride–sulfate drinking water and 250.00-500.00 mg/L
for bicarbonate drinking waters .On the other hand, It is also

American Journal of Applied Chemistry 2016; 4(5): 164-169 168
reported that in drinking water, the maximum level of
alkalinity, sodium, boron, and bromine are 6.5 mg/l, 200.00
mg/L, 0.50 mg/L and 0.01 mg/L respectively [12].
According to WHO, the range for hardness (calcium and
magnesium) in drinking water is 100.00-500.00 mg/L. The EC
standards also list numbers for calcium (guide level of 100 .00
mg/L) and magnesium (guide level of 30.00 mg/L) [21].
The best tasting drinking water for most consumers contain
about 10.00-100.00 mg/L total hardness as CaCO3 and a TDS
of about 150.00-250.00 mg/L [7]. As per summary of the TDS
or TH or minerals level in safe drinking water, the quality can
be categorized in several groups as given below; [7, 12, 17]
Poor : less 100.00 mg/L
Excellent : 100.00 to 300.00 mg/L
Excellent : 300.00 to 600.00 mg/L
Fair : 600.00 to 900.00 mg/L
Poor : 900.00 to 1200.00 mg/L
Unacceptable : Greater than 1200.00 mg/L
The obtained results for TDS in the present work range is
from 9.44 -335.00 mg/L (Table-2). It is clear that the TDS
level (335.00 mg/L) of only one company (company 2) is
satisfactory whereas that of other companies are much lower
than the standard. It is to be noted that the level of TDS
(9.44mg/L) of one company (company 6) is abnormally low.
Similarly , the result of TH (Table -2) obtained in the range of
4.35-150.38 mg/L as CaCO3. It is also observed that the level
of TH of water is not agreeable whereas that of other company
are lower than the standard. In this studied company’s water
samples, company 6 is strangely low.
It has been seen a scenario in their water processing unit, they
release healthy (Ca2+, Mg2+, Na+,CO3
2-,HCO3
-,Cl-,& SO4
2-)
and unhealthy toxic (Pb2+, Zn2+, As3+, CN-, Cd2+, Cu2+, & NO2
2-)
minerals from the raw water by using the Reverse Osmosis
system. They never balance necessary minerals level in
drinking water according to the demand of human body.
Table 1. BSTI Guideline for Mineral Drinking water (Physical, Chemical & Microbiological)
Sl/No. Parameters Unit Bangladesh Standard Value (BDS-1240,2001 BSTI)
Physical Test
1 Colour Hz < 5.00 (Max.)
2 Taste - Agreeable
3 Odour (Cool & Hot) - Unobjectionable
Chemical Test
1 pH - 6.40~7.40
2 Total Dissolve Solids(TDS) mg/L <500 (Max.)
3 Total Conductivity µS/cm <800 (Max.)
4 Salinity mg/L <450 (Max.)
5 Total Hardness as CaCO
3
mg/L <300 (Max.)
6 Chloride (Cl-) mg/L <250 (Max.)
7 Arsenic (As) mg/L <0.01 (Max.)
8 Total Iron (Fe) mg/L <0.30 (Max.)
9 Nitrate (NO
3
-) mg/L <4.50 (Max.)
10 Free Carbon dioxide mg/L <0.05 (Max.)
Biological Test
1 Total Coliform in 100 ml cfu Absent
2 Fecal Coliform in 100 ml cfu Absent
3 Plate Count in 1 ml cfu <1000 (Max.)
Few experts’ responses about low mineral drinking water
are as follow;
WHO’s Dr. Gala-Gorchev states that WHO has “no
information that low minerals water would have an adverse
effect on minerals balance” [12, 21]
US EPA’ Dr. Edward V. Ohanian, Chief of Human Risk
Assessment Branch Wrote:
“Drinking water supplies a number of minerals that are
important to human health. However, drinking water is
normally a minor source of these minerals. Typically, the diet
is the major source of these beneficial minerals. I am not
aware of any data adequate to support the conclusion that
Water with lower levels of mineral is unsafe”. Beside this, U.S
Army does not consider lower mineral (less than 100 mg/L) to
be a problem and have no minimum [12].
5. Conclusion
More than one hundred drinking mineral water (pet bottle)
plants are established in Bangladesh in short time. They are
selling drinking water to the public through confectionery
shops and other retailers in different places including bus &
railway stations. In hot seasons, most of the peoples become
thirsty and they need water containing minerals to drink
especially when they work hard and walk. But they do not get
the sufficient minerals to drink it from the bottled water sold in.
As a result, they are depriving of the natural mineral. The
drinking water quality of most of the companies under the
present study does not meet the requirements regarding TDS
and TH. Drinking water manufacturer and user might pay
attention to improve the quality of drinking water based on the
finding from the study.
Finally, the followings can be quoted from the study
especially for the manufacturers and users;

169 Mohammad Rafiqul Islam et al.: A Study on Total Dissolved Solids and Hardness Level of Drinking
Mineral Water in Bangladesh
A. Read the label before buying to see its content.
Generally, most brands have reasonable amounts of
minerals that will not give any undue disadvantages
B. Buy only new production bottled mineral water and not
old stock to reduce any chances of leached chemicals.
C. Do not leave bottled mineral water in an area exposed to
direct sunlight or heat, such as in parked cars on a hot
sunny day.
However, it should be remember that not all brands are the
same. Mineral water comes from many sources and will not
taste the same or have the same mineral content.
Table 2. Analysis results in mg/L of TDS and TH in Drinking Mineral Water (PET Bottles).
Company→ Company-1
Company-
2
Compnay-
3
Company-4
Company-
5
Compnay-
6
Compnay-
7
Compnay-
8
Total Dissolve Solids
(TDS) as mg/L 140 335 *80.50 119.1 101 **9.44 *82.00 *90.00
Total Hardness as CaCO3
mg/L 72.78 150.38 *38.48 56.5 35.75 **4.35 *40.00 *45.85
Figure 4. TDS level at the different drinking bottled water in Dhaka City.
Figure 5. TH level at the different drinking mineral water bottle in Dhaka
City.
References
[1] http://www.bbs.gov.bd/WebTestApplication/userfiles/Image/N
ational%20Reports/Union%20Statistics.pdf
[2] http://www.bsti.gov.bd/list.html
[3] https://www.wqa.org/Portals/0/Technical/Technical%20Fact%
20Sheets/2015_TDS.PDF
[4] https://www.scribd.com/document/123925413/Model-Terms-o
f-Reference-Diagnostic-Water-Market-Assessment-for-Dhaka-
Water-Supply-and-Sewerage-Authority
[5] http://www.who.int/water_sanitation_health/dwq/nutrientscha
p12.pdf
[6] http://www.szu.cz/uploads/documents/chzp/voda/pdf/hardnes
[7] http://healthycanadians.gc.ca/publications/healthy-living-vie-s
aine/water-dissolved-solids-matieres-dissoutes-eau/alt/water-d
issolved-solids-matieres-dissoutes-eau-eng.pdf
[8] https://www.health.ny.gov/environmental/water/drinking/colif
orm_bacteria.htm
[9] https://mcb.berkeley.edu/courses/mcb135e/kidneyprocess.html
[10] http://gsdl.easternuni.edu.bd/greenstone/collect/7eufacultypub
/index/assoc/HASHae8d.dir/doc.pdf
[11] http://www.waterproblemsolvers.com/files/QuickSiteImages
TB-ConsumptionLowTDS.pdf, Reviewed by Dr. Lee T
Rozelle, Dr. Ronald L.Wathen, M.D.
[12] https://www.wqa.org/Portals/0/Technical/Technical%20Fact%
20Sheets/1993_ConsumptionOfLowTDSWater.pdf, (Water
Quality Association Science Advisory Committee
1992-1993,USA)
[13] https://en.wikipedia.org/wiki/Reverse_osmosis
[14] http://www.wellsysusa.com/wellsysusa/pdfs/7%20%20Safe
water%20org%20RO%20ultrafine%20nano%20comparision
.pdf
[15] https://www.epa.gov/quality/total-dissolved-solids-tds-epa-me
thod-1601-gravimetric-dried-180-degrees-c
[16] https://www.epa.gov/sites/production/files/201506/documents/
130_2dqi_crf.pdf
[17] http://www.who.int/water_sanitation_health/dwq/chemicals/td
s.pdf
[18] http://wqaa.gov.in/WriteReadData/UserFiles/Documents/Wate
rQualityStandards.pdf
[19] https://www.canada.ca/en/health-canada/services/publications/
healthy-living/guidelines-canadian-drinking-water-quality-gui
deline-technical-document-total-dissolved-solids-tds.html
[20] http://www.waterbenefitshealth.com/reverse-osmosis-water.ml
[21] http://www.who.int/water_sanitation_health/dwq/chemicals/ha
rdness.pdf
[22] http://www.rpi.edu/dept/chem-eng/Biotech-Environ/Projects0
0/memfilt/kidneys.htm