Def Sci J, Vol 35. No 1. January 1985, pp 71-88
Fluoride in Drinking Water .Its Effects and Removal
RAM GOPAL & P.K. GHOSH
Defence Laboratory, Jodhpur-342001
Received 11 August 1983, revised 24 December 1983
Abstract. Occurrence of fluoride in water, its metabol~sm, excretion. effect o
ingestion in human and cattle systcm .,nd methods of fluoridation and defluorida-
tion have been discussed. The presence of fluoride rn waters occurring in India,
with special reference to Raj~sthan desert has been reviewed. Based on the
survey and physico-chemical analyses of about 2,700 water samples of Rajasthan,
distribution of fluoride in this area has been d~scussed wrth reference to drinking
water standards. A water resources map showing concentrations of fluoride in
four arid districts of Rajasthan is also presented.
The Government of India, during the International Drinking Water Supply and
Sanitation Decade, (1 98 1 - 1990), has undertaken to supply safe drinking water for the
country's urban and rural population. T t is reported1 by WHO in 1981 that approxi-
mately three out of five persons in the developing countries do not have access to safe
drinking water. The urban areas are better served, 75 per cent of the population
having some form of water supply through house connections or stand pipes while only
29 per cent have equivalent water supply in rural areas.
Fluoride has been reported by health organ is at ion^^-^ as a health affecting substance.
It has been recommended as an essential substance in water for building healthy
teeth at levels within 1 mg/l concentrations. The maximum permissible limit of
fluoride in water has been laid down as 1.5 mg/l by WHO and ICMR and 0.7 to 1.7
mgll by USPHS. The effects of fluoride in drinking water have been studied in detail.
Consumers exhibiting positive symptoms after taking such water have attracted the
attention of the medical profession. The research works-"
the introduction of fluoridation, began as an investigation into the cause of mottled
teeth in certain communities in USA. Much work has been reported by Deanl2'lS and
Elvove14 on the relation between mottled teeth (dental fluorosis) and the fluoride level
which led ultimately to
Ram Gopal & P K Ghosh
In India, a disease in humans similar to mottled enamel was first reported by
Vishwanathan15 to be prevalent in Madras Presidency in 1933. Mahajan16 reported a
similar disease in cattle in certain parts of old Hyderabad State. However, Schortt17
was the first to identify the disease as 'fluorosis'. Subsequent to these findings, cases
of fluorosis have been reported from several other parts of the country.
The arid zone in India occupies nearly 12 per cent of the total area sustaining a
human population of over 19 million and livestock over 23 million, The Thar
desert, extending 4.46 lakh sq. km. in India and Pakistan territories, is covered with
wind blown sand and sand dunes. Rajasthan desert covers an area of 1.96 lakh sq.km.
Defence Laboratory, Jodhpur (DLJ) is monitoring the water quality of this area since
1960 and our studies have shown that the ground waters are generally brackish.
Further, fluoride and nitrate are present throughout. The national objective is to
provide safe and adequate water supply of proper quality to all the 1,53,000 problem
villages by 1990. A problem village has been roughly defined as one which has no
water source of its own and the nearest one is 1.6 km. or more away, Most of the
villages of arid zone of Western Rajasthan fall under this category. Construction of
well or tubewell costs about Rs. 50,000 in south-west portion and about Rs. 1.5 lakh
in other parts. A water supply scheme at village level would cost about Rs. 5 lakhs.
In this paper, the chemistry of fluoride, its occurrence in water, metabolism,
excretion, effect of ingestion in human systems and methods of fluoridation and
defluoridation have been discussed. Occurrence of fluoride in Indian waters and
detailed studies on ground waters of Rajasthan with special reference to desert waters
have also been reviewed and some comments offered on permissible limit of fluoride
in water. Scope for further investigations in the area is indicated.
2.1 Concentration of Fluoride in Water
Surface waters generally do not exceed 0.3 mg/l of fluoride unless they are polluted
from other source^^^'^^. Extremely high fluoride concentrations (greater than 1000
mgl I) in surface waters, however, have been found where fluoride- rich volcanic
rocks are c~mmon~~'~'.
The average concentration of fluoride in sea water2* is about
1.35 mgll. Values ranging from 1 to hundreds of mg/l have been reported in geother-
mal fluid^^^-^^. But fluoride in surface waters of peninsular India covering a few
important rivers, streams and springs have been found by DeshmukhZ6 to go up to 3
mg/l in Godavari bed, Andhra Pradesh, 3.5 mgll in Chitravati and Tambraparni
beds, Tamil Nadu and 12 mg/l in Kongal, Nalgonda, Andhra Pradesh.
Many workers have reported fluoride bearing waters in Andhra Prade~h~~-",
Punjab and HaryanasO*", Maharashtras2, Tamil N a d ~ ~ ~ ,
pradeshs4, Gujarats6, Uttar Pradesh3=, BihaF and Kerala and Lakshadweepss. RaoS8
Table 1. Fluoride concentration in different states of India
Range of Fluoride in Ground Waters in Different Places (mgll)
1.5-4.0 Region 0-1.5
4.0-8.0 More than 8.0
Madurai, North Arcot,
Kerala Quilon, Alleppey
Mehasana, Surendra Nagar,
Western parts of
Southern part of Kutch
Dist., Western part of
Parts of Ganganagar. Churu,
Nagaur, Alwar, Bharatpur,
Jaipur, Tonk, Jalore,
Sirohi, Pali, Barmer,
Jaisalmer, Bikaner and
Parts of Jhunjhunu,
Sirohi, Pali, Jalore,
Churu, Jaipur, Nagaur,
Bikaner and Jodhpur;
Parts of Ganganagar
Nagaur. Sirohi, Jalore,
Pali, Jodhpur, Bikaner
Barmtr and Jaisalmer.
Parts of Haryana
Fluoride in drinking water
reviewed the above results and categorised the areas into four groups showing the
concentrations in the range of 0-1.5, 1.5-4.0, 4.0-8.0 and over 8.0 mg/l. Data are
presented in Table 1.
2.2 Distribution offluoride in ground water of Rajasthan
Out of 27 districts of Rajasthan 16 districts (Table 2) have fluoride bearing waters in
concentration more than the permissible limit of 1.5 mgJl laid down by WHOa9.
Saxena4O reported that in Rajasthan 6,000 villages (out of 33,000) have water with
fluoride concentration exceeding the permissible limit and that dental and skeletal
fluorosis is wide-spread in these ~illages~l'~~.
~o-authors~~-~~ conducted extensive survey of Rajasthan desert and reported the
incidence of fluoride in ground waters of arid areas based on physico-chemical,
toxicological and epidemeological studies. A number of worker^*^-^^ have also
reported fluoride toxicity in ground waters of Rajasthan. Analyses of about 2700
water samples by the authors and other workers indicate that the fluoride concentra-
tion in some pockets is alarming and needs immediate attention.
During the last decade, Gopal and
Table 2. Maximum concentration of fluoride in 16 districts of Rajasthan (mg/l)
Districts No. of samples Fluoride concn.
As part of our regular programme, survey and assessment of water quality
supplied to services have been carried out by undertaking detailed studie~~~'~"
1300 water samples from four arid districts of Barmer, Jaisalmer, Bikaner and Jodhpur.
Ram Gopal & P K Ghosh
Some relevant parameters - pH, TDS, alkalinity, and fluoride are given in Table 3.
Percentage frequency of ground waters of this area having different fluoride ranges
is ppsented in Table 4. A water resources map (Fig. 1) showing distribution of
fluoride in waters of these arid districts is also discussed. The map indicates the
areas of high fluoride (> 10 mg/l), medium fluoride (4 - 10 mgll) and low fluoride
levels (2 - 4 mg/ 1), and areas containing potable water (F c 2 mg/ 1).
Table 3. Physico-chemical characteristics of ground waters of Barmer, Jaisalmcr,
Bikaner and Jodhpur districts of Rajasthan
Barmer Jaisalmer Bikaner Jodhpur
TDS (mg/l )
0.2- 10.9 Traces-8.0 Traces-20.0 Traces- 1 1.2
Table 4. Percentage frequency of ground waters of Barmcr, Jaisalmer, Bikancr
and Jodhpur having different, fluoride ranges
1.5- 2 11
Above 10 3
Fluoride range (mg/l) Barmer Jaisalmcr Bikancr Jodhpur
3. Drinking Water Standards for Fluoride in Water
The first presentation of water quality standard was made in 1914 by USPHS. The
fluoride concentration laid down by USPHS (1962)59, WHO (1963)54, and ICMR
(1962)65 have been amended (Table 5). The Ministry of Health, Govt. of
has prescribed 1.0 and 2.0 nlg/l as permissible and excessive limits for fluoride in drink-
ing water. The USPHS drinking water standards of 1962 get a mandatory limit of
fluoride based on the annual average of maximum daily ambient temperature
as given in Table 6. The fluoride-temperature relationship is based on the premise
that children drink more water in warm climates, and therefore, the fluoride
content in the water supply should be reduced to prevent excessive total fluoride
~ ~ n ~ ~ m p t i o n ~ ~ - ~ ~ .
Fluoride in drinking water
0 - 2
2 - 4
4 - 10
Figure 1. Distribution of fluoride in ground waters of four arid districts of
Among the many methods suggested for determination of fluoride ion in water
given in the official British and American Compilation of Methods, the calorimetric
and electrode methods are the most satisfactory at the present times0.
The role of fluoride in animal or human metabolism is not known with certainity.
The element is metabolised from both electrovalent and covalent compounds.
Fluorine in small quantities is essential for the formation of caries-resistant dental
enamel and for the normal process of mineralisation in hard tissuess1. Fluoride
inhibits several enzyme systems, diminishes tissue respiration and anaerobic
glycolysis. Low fluoride concentrations stabilise the skeletal system by increasing
the size of the apatite crystals and reducing their solubility. The great affinity of
fluorine for calcium phosphate is perhaps the most important from the physiological
Ram Gopal & P K Ghosh
Fluoride in drinking water
Table 6. USPHS drinking water standard : recommended limit of fluoride
Annual average of maximum
daily air temperature
Recommended control limits
of fluoride (mg/l)
Lower Optimum Upper Limit
Sources : Drinking Water standards and guidel~nes, Water Supply Division. @PA,
point of view; it results in its accumulation in all tissues exhibiting physiological
or morphological calcification. About 95 per cent of the fluoride in the body is
deposited in hard tissues and it continues to be deposited in calcified structures even
after other bone constituents (Ca,P,Mg,CO, and citrate) have reached a steady state.
A pattern broadly similar to that in bone is followed in the fluoride concentrations
in teeth. However, the uptake almost ceases in dental enamel after the age
of about 30 years.
4.1 Efects of Fluoride Ingestion in Human and Cattle
The chronic toxic effects (fluorosis) of excessive intake of fluoride are usually observed
as skeletal abnormalities or damage. Many detailed medical investigations have
confirmed that there is no adverse effect on the body from continuous long-term con-
sumption of 1 mgll of fluoride in drinking watera2. Mc Clureaa has computed for
children of various age groups the total daily intake of fluorides from food and water
and established the following facts concerning the mottling of teethe4.
4.1.1 Mottled enamel can be produced only during the period of calcification of the
teeth. In other words, after about 12 years, mottled enamel cannot be produced
whatsoever the level of fluoride in the water.
Figure 2. Fluorosis of teeth
Rarn Gopal & P K Ghosh
4.1.2 Once such lesions are formed they cannot be repaired, either during the calci-
fication or thereafter.
4.1.3 Fluoride appears to be the only agent that is ordinarily a part of the diet
which has an effect on enamel production.
4.1.4 After calcification is completed the structure of the enamel remains unaltered
despite changes in diet.
It has been established that physiology of human skeletan is not adversely affected
by fluoride up to a level of 8 mgll in drinking wateres. Ingestion of 20-30 mglday
or more through water over a period of 10-20 years results in crippling fluorosis and
severe osteosclerosis. Calcification of certain ligaments, rendering movements of
joints difficulto6, is usualiy associated with atleast 10 mg/l of fluoride in drinking
water. A WHO reportn7 and studies of Smith andH edge" have also related con-
centration of fluoride to the biological effects. The above studies report the effects on
thyroid at 50 mgl I , growth retardation at 100 mg/l and kidney changes at 120 mg/l
concentration of fluoride. The bone structure was found to be blurred and it becomes
a diffuse structureless shadow with uneven contours. These changes were marked
in the spine and ribs. The acute lethal dose for man is between 2.5 and 5.0 gm
depending upon the solubility of the compound and susceptibility of the man.
Effects of fluoride on animals are analogous to those on human beings. Studies
in Australia have shown the development of exostosis of the long bone and mandi-
bles in mature sheep, as well as the abnormal development and wear of teeth erupted
by young sheep exposed to excessive fluorideos.
4.2 Excretion of Fluoride
Fluorides are excreted through urine, faeces, sweat, and other body fluids. Urine
of an average adult living in fluoridated water supply areas usually accounts for
the principal excretion of fluorides eliminating 5.0 mg of fluoride daily70. Fluorides
appear rapidily in urine after ingestion and generally the level reflects the daily
intake. Depending upon the diet, the faecal excretion accounts for 10-30 per cent
of the daily intake. Sweating may account for as much as 50 per cent of the total
fluorides excreted in hot climateg5"'.
4.3 FIuoride and Dental Caries
Fluoride is the only halogen which combines with hydroxyapatite to form fluoroapatite
structure in the tooth enamel making the tooth stronger and stable to acid. This
chemical crystalline change occurs after 5-6 years of age and then exists for the life of
the t o ~ t h ~ ~ * ' ~ . Fluoride supplements become necessary for children living in areas having
unfluoridated drinking water. Oral fluoride supplements are given in the form of tablets,
drops, lozenges, fluoridated salt and multivitamin combinations. Flouride supplements
Fluoride in drinking water
during pregnancy have no conclusive beneficial effects since the crossover through
the placental barrier of fiuoride is minimal. Topical fluorides including gels and
toothpastes do not compare well with ingested flourides in caries prevention. However
30-40 per cent reduction in dental caries has been shown by use of such preparations.
Toothpastes contain 0.4 per cent stannous fluoride, 0.22 per cent sodium fluoride
or 0.76 per cent monofluorophosphate, the last being the one more popularly used in
our country. It has been shown that constant use of toothpaste reduces caries inci-
dence by 15-30 per cent. Like the fluoride toothpastes, mouthrinses and mouthwashes
containing 0.2 per cent sodium fluoride cause toxic symptoms.
Optimum concentration of fluoride intake from water for any temperature can be
calculated by a generalised formula74.
Optimum F =
where E = (-0.038 + 0.0062 t ), is the estimated daily average water consumption
for children of ten years of age in terms of ounces of water per pound of body weight
and t is the annual mean of daily maximum temperature ("F).
pean countries. Opposition to fluoridation has also been raised from time to time.
During the last three decades hundreds of studies have been undertaken to correlate
the concentration of waterborne fluoride and the incidence of dental caries. Health
authorities throughout the world have endorsed that fluoride in drinking water pre-
vents dental caries and controlled fluoridation is an acceptable public health measure.
Recent studiesT6 have indicated that fluoride also benefits older people in reducing
prevalence of osteoporosis and hardening of arteries.
is done in drinking waters in a number of European and non-Euro-
5.1 Chemicals Used
The three most commonly used fluoride compoundsT7 in water treatment are sodium
fluoride, sodium silicofluoride and fluosilicic acid, also known as hydrofluosilicic,
hexafluosilicic or silico-fluoric acid. Besides these chemicals for fluoridation of water,
others are hydrofluoric acid (HF), fluospar (CaF*), ammonium fluosilicate [(NH4),
SiF,], magnesium fluosilicate (MgSiF,. 6H20) and stannous fluoride. Out of these
only stannous fluoride is used in America owing to insufficient evidence about the
long term effects of the other reagents. Ammonium and magnesium fluosilicate pose
the danger of overdosing. Fluospar is insoluble as such but soluble in the presence of
AI, (Sodr and therefore its use is restricted. HF is highly corrosive and difficult to
handle. Personal safety78 in handling fluoride chemicals, limitation on dose of che-
micals, provision of proper feeders for powder or liquid forms of chemicals and re-
gular medical examination of workers etc. should be carried out.
Ram Gopal & P K Ghosh
A variety of methods for fluoride removal are
into two categories, viz precipitation and adsorption.
They can be divided
6.1 Precipitation methods
Methods involve the addition of chemicals and the formation of fluoride preci-
pitate or co-precipitates. The chemicals employed include lime, magnesium com-
pounds and aluminium sulphate. Lime (CaO) is the cheapest chemical employed
for the removal of fluoride from water.81 However, large amounts of fluoride
are removed by reaction with calcium oxide followed by reaction with susperphos-
phate and calcium oxide or aluminium sulphate for the removal of residual fluoride.
Based on this principle a number of w~rkers~'-~~
aluminate, iron salts, alum and polyelectrolytes for coagulation. The well-known
Nalgonda-techniques7 involves the addition of lime powder and bleaching powder
(for disinfection) first and after thorough mixing with water, the alum solution is
poured and stirred for 10 minutes. The contents are allowed to settle for one hour
and the clear water is withdrawn. When magnesium hydroxide, magnesia and calcined
magnesite were used along with lime, the fluoride removal capacity was fo~nd~~'~~-!''
to be better. Empirically the amount of fluoride removed is given by 0.07F 2/Fg,
where F represents fluoride initially present in mg, and Mg the magnesium removed
in the form of flocks (mg).
studied the use of lime or sodium
The drawbacks of the precipitation method include the necessity for additional
reagents, higher transportation and treatment costs, and the large volume of sludge
produced. Filter alum is not economically feasible in some cases because of dosage
6.2 Adsorption methods
a contact bed. Fluoride is removed by ion exchange resinsa2 and adsorbents like
zeolites, phosphatic compounds with hydro~yapatite~~'~~-~~
activated carbonss, Defluor~n-I~~*~~, Defl~oron-2~~*~~,
the passage of the fluoride containing water through
There are no known commercial anion exchange resins which are selective for fluoride
only. Polystyrene anion exchange resins in general and strongly basic quarternary
ammonium type resins in particular are known to remove fluorides from water along
with other ani~ns'~'-'~~. Cation exchange resins impregnable with alum solution
have been found to act as defluoridating agentslOa. Venkatraman et allo4 reported that
'Avaram Bark' based cation exchange resins are effective in removal of fluoride from
water. Active carbon prepared from spent coffee husk'05, coconut shelllo" saw-dust'07
and their sulphonated compounds with alum have also been found to remove
Fluoride i n drinking water
Water with high fluoride (> 10 mg/l) concentration can economically be treated
by split treatment using lime and alum in two stagesa1. Adsorption methods are
usually appropriate for relatively low concentration of fluoride (10-20 mg/l) after the
removal of fluoride by precipitation method to the 10-20 mg/l level.Io8
7. Fluoride Levels in Waters of Rajasthan Desert and Some Comments
Detailed studies on 13 17 water samples of arid districts of Jaisalmer, Barmer, Bikaner
and Jodhpur (Table 3) have shown that about 9 per cent waters are potable con-
sidering 500 mg/l total dissolved solids limit laid down by WHO and ICMR. It is
observed that TDS varied between around 100 and 30,000 mg/l. The waters are
generally brackish and alkaline having pH between 6.6 and 9.0. It is found that
alkalinity due to carbonate is practically nil and very few samples were found to
contain the maximum value of 190 mgp. The alkalinity due to bicarbonate is found
to be as high as 3920 mg/l in Jodhpur district.
All the waters have been found to contain fluoride and a maximum value of 20
mg/l was found in Bikaner. Rao'09 observed that natural waters having toxic amounts
of fluorides are usually associated with alkalinity (as CaCO,) in the range of 400-1000
mg/l. The arid waters of Rajasthan in general have shownl10 similar characteri-
stics of excessive fluoride with high salinity and alkalinity. Optimum alkalinity level
in the four arid districts have been found to vary from 1956 to 3920 mgll. It is
seen from Table 4 that about 47 per cent waters fall ~ithin the permissible limit
of 1.5 mg/l of fluoride. For fluoride level exceeding 10 mgl1 the frequency of samples
is about 7 per cent. Saxenado and G0pal~~'-6 et a1 have shown the occurrence of dental
and bone fluorosis in the areas having excessive fluoride concentration. Continuous
withdrawal of groundwater and depletion of water sources particularly in summer
months have been shown to further increase the fluoride concentration. The above
findings are in agreement52*109 with recent surveys undertaken by Rajasthan Ground
Water Ilepartment, Public Health Engineering Department, Rajasthan and Zonal
Laboratory, National Environmental Engineering Institute, Jaipur.
Gopal et a14a-46'110-113
detailed survey and physico-chemical, toxicological, microbiological and desalination
studies of brackish waters of Thar desert. It has been found that local population
of the arid-areas is consuming for generations waters having TDS, 2000-3000 mg/l
and fluoride up to 2 mg/l without any apparent deleterious effects. It is also gathered
from Public Health Engineers, that a number of waterworks in Rajastan and Gujarat
are supplying waters having fluoride up to 2 mg/l. Ministry of Health, Govt. of
Indiaa1 has also prescribed 2 mg F/I as the excessive limit in drinking water. In
view of the scarcity of potable waters in arid districts of Rajasthan based on our
studies and drinking water practices, this laboratory has recommened the maximum
allowable limit of fluoride and TDS be extended up to 2 mgJl and 2000 mg/l
have reviewed the last 20 years work undertaken on the
Rum Gopal & P K Ghosh
respectively for potable water of these areas. With such relaxed limits of fluoride,
60 per cent of waters of these arid districts may be considered fit for consumption.
i) Fluoride bearing waters have been reported in Andhra Pradesh, Maharashtra,
Punjab, Haryana, Tamil Nadu, Karnataka, Madhya Pradesh, Gujarat, Uttar Pradesh,
Kerala and Lakshadweep. Some parts of a few states are fluorosis endemic areas.
It is found that fluoride is widely distributed in waters Rajasthan. Dental and bone
fluorosis are wide spread in 6000 villages of Rajasthan.
ii) Sedimentary rocks of limestone and sandstone formations having fiuorspar
(CaFz) are the main contributors of fluoride in ground waters of arid region. Quality
of water of Thar desert is far from satisfactory. The ground waters of western
Rajasthan are generally brackish having high salinity up to 10,000 mg/l (as NaCI)
and high amounts of Sodium. Alkalinity due to carbonate is practically nil but
bicarbonate (pH up to 9) is present in high concentrations (as high as 3920 mgll).
Residual sodium carbonate is high in fluoride bearing ground waters than the
maximum limit of 2.5 mgll.
iii) In general there exists a good linear positive relationship between Fand HCOs
ions and negative relationship between F and Ca + Mg ions in high fluoride
bearing ground waters. Most of these high F waters due to very high Nu fall under
high to very high alkali hazard waters.
iv) Methods of removal of fluoride have been enumerated in order to control
excessive intake of F.
v) Based on detailed studies this laboratory has re~ommended'l'~"~
in the limit for F from 1.5 to 2 mgp and TDS from 1500 to 2000 mgp for desert
waters. Water resources maps showing quality and quantity of water of arid areas
have been prepared and found useful by local population, survey parties, armed
forces and BSF deployed in this area.
9. Proposals for future studies
i) Water resources maps showing pockets of allowable concentrations of F and
problem areas are required to be prepared district wise. The consumers should
be educated on the beneficial and ill effects of this health affecting ion.
ii) Defluoridation schemes should be undertaken at Central and State Government
levels particularly in areas where water is scarce and highly fluoridated.
iii) Detailed studies are required to be undertaken to establish correlation between
the alkalinity and incidence of fluorosis as found in this study.
Fluoride in drinking water Download full-text
iv) The important weak hydrogen bonds formed between amides in biological systems
fluoride in the formation of much stronger bonds between
F and amides. These raise the fluoride blood level and interfere in the healthy
operations of living systems. The study needs immediate attention.
Fluoride blood levels in cattle and F content fixed in foodstuffs grown in fluoride
bearing waters have not been studied. Rajasthan and Gujarat, the F prone
states are one of the major suppliers of meat, milk and milk-products. The
biochemical studies for fixation of F in these consumable products from F
bearing waters and fodders etc. are required to be conducted country-wide to
control the excessive P intake, which is being received from a growing number
of sources 11s*116-
vi) Not ignoring the beneficial effects of fluoridation up to 1.5 mg/l in drinking water
in deficient areas indiscriminate use of F containing dental products like
dentalgels and toothpastes, tablets and mouthwashes should be controlled
immediately in endemic areas.
vii) Monitoring of water quality should be continued for F also using simple and
rapid tests incorporated in field testing kits as undertaken by this laboratory
with one such kit developed recently11g.
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2. U.S.S.R. All Union State Standard 2874.73.
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3. 'Guidelines for Canadian Drinking Water Quality, 1978' (Health and Welfare Canada.
Ottawa, Canada), 1979,
4. Tale, C. H. & Trussell, R. R., Jour, AWWA, 69 (1977).
5. Taylor, F. B., Jour. of New England Water Works Association, 91 (1977).
6. Eager, J. M., Pub. Health Rep., 16 (1901), 2576.
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8. Hannan, F., Wat. Works. Engng, 79 (1926) 934.
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I I. Smith. M. C., et al, 'Cause of Mottled Enamel a Defect in Human Health', (Tcch,
Bull. No. 32. Univ. Arizona, USA), 1931.
12. Dean, H. T. & Elvove, E., Pub. Health Rep., 50 (1935). 1719.
13. Dean, H. T., Pub. Health Rep., 53 (1938). 1443.
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New Delhi, 1935. (Quoted from Indian Institute of Science. 33A, 1. 1951).
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Research, New Delhi, 1934.
17. Shortt, W.E,, Indian Medical Gazette, 72 (1937). 396.
18. Barnett, P. R., Jour. AWWA, 61 (1969), 61.
19. Livingston, D. A,, 'Chemical Composition of Rivers and Lakes', U.S.G.S. Prof. Paper
Decree No. 1972 of the State Committee