potable water sources and methods of purification at domestic level

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POTABLE WATER
Sources andmethods of purification at domesticlevel
Out of all the water(71 percentcoverof earth) onearth,saline waterinoceans,seasandsaline-
groundwatermake upabout97%. Only2.5.2.7% isfreshwater,including1.75 – 2% frozeninglaciers,ice
and snow. 0.5 – 0.75% is available as fresh groundwater and soil moisture, less than 0.01 percent is
available as surface water in lakes, swamps and rivers.
Fresh water is any naturally occurring water except seawater and brackish water. Fresh water
includeswaterinice sheets,ice caps, glaciers, icebergs, bogs, ponds, lakes, rivers, streams and ground
water. Fresh water is generally characterized by having low concentration of salts and other total
dissolved solids. Technically fresh water can be defined as water with less than 500 ppm of dissolved
salts.i
Some sources also describe the upper limits of salinity as 1000 – 3000 ppm.iiiii
Fresh water is not the same as potablewater (drinkingwater).Much ofearth’s fresh water (on surface
and groundwater) is unsuitable for drinking. This unsuitable fresh water can be made potable with
various types of treatment.
Throughouthistory,waterhasbeencrucial forsustaininglife,bothforhumansandother
organisms,makingita significantfactorforlife onearth.There are manyareas inworldwhere humans
do nothave access to sufficientpotable waterorrelyonwater sourcesthatare contaminatedwith
toxins,suspendedsolids,pathogens,ordisease vectors.Consumingthiswaterorusingitto cook can
leadto bothchronicand acute illness,whichisone of the majorcausesof sufferingandevendeath
aroundthe world.Therefore,reducingwaterbornediseaseswithdevelopingsafe (potable water)has
become a majorgoal for publichealth, particularlyindevelopingcountries.
What ispotable water?Potable wateriswaterwhichhasbeenfiltered,cleanedortreatedto
meetthe standardsof drinkingwater,meaningthatitisreasonablyclearof contaminantsandharmful
bacteria.Thismakesthe watersafe for drinkingandcooking. Accordingof BIS(Bureauof Indian
Standards)iv
(IS10500: 2012 )levelsof some of the parametersare asfollows
Sl.No. Characteristics Acceptable limit Upper limitinabsence of alternative sources
1. pH 6.5 – 8.5 No relaxation
2. Taste Agreeable Agreeable
3. TSD (mg/L) 500 2000
4. Turbidity,NTU 1 5
5. Total hardnessas
CaCO3 (mg/ml)
200 600
6. E. Coli Shall notbe
detectedinany
100 ml sample
Shall notbe detectedinany100 ml sample
7. Total Ironas Fe
(mg/ml)
0.3 Relaxation
8. Odour Agreeable Agreeable
Thisstandard hastwo limitsi.e.acceptable limits and permissible limits in the absence of an alternate
source. If any parameter exceeds the limit, the water is considered unfit for human consumption.
Accordingto ministryof drinking water and sanitation (2013), more than 85% of rural households have

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access to drinking water within near their premises. This figure indicate a better scenario than the UN
reportof 1975, whichstatedthat 1230 millionpeople didnothadaccessto safe drinkingwatersupplies.
REQUIREMENTS/ HEALTH CONCERN
The amount of drinking water required is variable. It depends on physical activity, age, health and
environmental conditions.Itisestimatedthatthe average adultdrinksabout1litre of water a day which
is95% lessthan three litres per day. In hot climatic conditions up to 16 litres of water may be required
per day.v
Diseases caused by unfit water sources
Bacterial diseases: cholera, typhoid, dysentery
Viral infection: Hepatitis, poliomyletis
Protozoan infection: amoebiasis, giardiasis
Parasitic infection: taeniasis, ascariasis
MAIN SOURCES OF DRINKING WATER IN India 2011
SL. NO. SOURCE PERCENTAGE
1. Total source 100
2. Tap water (total) 43.5
3. Tap water– untreated 11.6
4. Tap water – treated 32.0
5. Well (total) 11.0
6. Covered well 1.6
7. Uncovered well 9.4
8. Hand pump 33.5
9. Tubewell / borewell 8.5
10. Spring 0.5
11. River/canal 0.6
12. Tank/pond/lake 0.8
13. Other sources 1.5
METHODS OF PURIFICATION AT DOMESTIC LEVEL
Treating fresh water/untreated water prior to consumption combats many illness such as dysentery,
typhoid, cholera etc.
1. STRAINING WATER THROUGH CLOTHvi
It iseasyto filterwaterusingcloth.Thiskindof filtrationwill eliminatethe mainsolidimpurities
from water as well as any insect larvae that it may contain. The cloth used, preferably cotton
mustbe thickenoughtoproperlyretainthe impurities. If it is too thick, then filtration will take
longer. It must always be washed before and after use.
Straining along is not a sufficient form of treatment. Nevertheless, straining water before
treating it using one of the other methods will significantly improve the quality of water
obtained
Advantages – simple to use; almost no cost; very useful or even essential for pre-treatment
purposes.
Disadvantages – does not eliminate the microbes, and chemical contaminants.

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2. THREE POT METHODvi
Thismethodservesthe same purpose asfiltrationbyremoving the main solid impurities found
in water. For improved efficiency, this method may be used to complement filtration.
Advantages – simple to use; almost no cost
Disadvantages – a summary treatment, that cannot make water drinkable; does not eliminate
the microbes, and chemical contaminants.
3. TREATMENT BY BOILINGVI
Boilingtoo isrelativelyeasytodo.It will kill all of the germsandmicro-organismspresent in the
water. To do so, first filter or decant the water, then bring it to a rolling – bubbling boil for at
leastone minute atlow altitude and for at least three minutes at altitudes above 2000 metres.
Boiledwatermaylack taste. This problem can be solved by vigorously shaking the water to re-
oxygenate it or by adding a little salt.
Advantages – easy to use; kills almost all pathogens
Disadvantages – requires fuel (approx 1 kg of wood per litre of water); relatively high cost
4. CHEMICAL DISINFECTION
A. TREATMENT BY CHLORINATIONVI, vii
Chlorination is a simple and effective way to disinfect water to make it drinkable. It
comprisesusingof chlorinatedproducts(chlorinetabs,bleach,etc.) intothe watertokill the
microorganisms in it. The water becomes drinkable after 30 minutes of treatment and
remains so for few days, depending upon the storage conditions.
Bleaching powder (CaOCl2)vii
– it is white amorphous powder with pungent smell of
chlorine,itrapidlylosesitschlorine contentonexposure tolight,airandmoisture but when
mixedwithexcessof lime,itretainsitsstrength(stabilizedbleach).Bleachingpowdershould
be stored in dark, cool and dry place in closed container. Highly turbid and polluted water
are not suited for direct chlorination, the rough estimation of application is 0.7 mg per litre
of water.
Chlorine solutionvii
– it may be prepared from bleaching powder, mixing 4 kg of bleaching
powder (having 25% available chlorine) in 20 L of water will give 5% solution of chlorine.

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Readymade chlorine solutionsare available in different strengths. The chlorine solution is
also subject to lose chlorine on exposure to light or prolonged storage.
High test hypochlorite (HTH or Perchloron)vii
– it isa calciumcompoundwhichcontains 60 –
70 percentavailable chlorine. It is more stable than bleaching powder, hence deteriorates
much less on storage
Chlorine tabletsvii
– available under various trade names e.g. Halazone tablets. Good for
small quantities of water
ADVANTAGES – muddy water can be made drinkable. If treatment is done properly, all of
the pathogens can be eliminated; chlorination has a durable effect.
DISADVANTAGES – handling risks involved, products must be obtained commercially.
B. IODINE TREATMENTvii
Iodine treatment may be used for emergency disinfection. Two drops of 2% of iodine
solutionperlitre of waterisrecommended. Contact time is of 20 – 30 minutes for effective
disinfection.Iodine does not react with ammonia or organic compounds, hence remains in
itsactive molecularformovera wide range of ph valuesandwater conditions; thus persists
longer than chlorine.
Advantages – persistslongerthanchlorine,isphysiologicallyactiveisused wisely according
to guidelines.
Disadvantages – careless use may lead to high concentration in drinking water, which may
lead to iodine poisoning.
C. POTASSIUMPERMANGANATEvii
It isa strongoxidizingagentand killscholeravibrio.Verylesseffective againstother disease
organisms.
Advantages – kills cholera causing vibrio
Disadvantages – altersthe colour,taste and smell of water;some standardshave declaredit
invalid for water disinfection
5. TREATMENT BY SLOW SAND FILTRATION
A sand filter is an eco-friendly water treatment tool that is relatively simple and costs little. It
works by letting the water percolate through a layer of sand. Two types of slow sand filtration
methods are used
A. PRE-TREATMENT SANDFILTERS – here the filterservesthe same purpose as straining water
through cloth. It is generally mmore effective,
Advantages – easy to use, low cost; suited for emergency situations
Disadvantages – allows only summary water treatment; only effective in providing pre-
treatment for solar, chlorination of boiling disinfection methods.
B. BIOLOGICAL SAND FILTRE (BSF)viii
It is a point-of-use water treatment system adopted from traditional low sand filters. It
removes pathogens and suspended solids from water using biological and physical
processesthattakesplace insand columncoveredwithabiofilm.BSFs have been shown to
remove heavy metals, turbidity, bacteria, viruses and protozoaixx
.

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Figure 1: basic diagram of a concrete biosand filtreviii
Accordingto IUPACdefinitionthe biofilm is – an aggregate of microorganisms in which the
cells are frequently embedded within a self-produced matrix of extracellular polymeric
substances (EPSs) adhered to each other.
A biofilm comprises any group of microorganisms in which cells stick to each other and
often to a surface. These adherent cells become embedded within a slimy extracellular
matrix that is composed of extracellular pylymeric substances.
Types of biosand filters
a. Concrete type
b. Plastic type
c. Stainless steel
Advantages – removes pathogens and suspended solids; long period efficiency, low cost
Disadvantages – complex maintenance.
6. TREATMENT WITH CERAMIC FILTERS
Ceramicfiltershave beenusedtotreatwaterformanycenturies.Dependingontheirtype,small
fixedinstallations or transportable devices are used to filter water. They often take shape of a
pot or a bowl and are impregnated with fine silver colloidal particles serving as disinfectant,
stopping the bacterial proliferation in the filter. The filter is installed in a 20-30 L container.
Advantages – easy to use, long life, fairly low cost when filter is made locally
Disadvantages – low production rate (1-2 L per hour); requires filter maintenance (using a
cleaning brush)

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Figure 2: ceramic filterxi
Figure 3: ceramic filterxii
7. SODIS(solarwaterdisinfection) METHOD
Thismethodisperfectfortreatmentof drinkingwaterindevelopingcountries,asitrequires
onlysunlightandlightweighttransparentplasticbottlesmade upof PET(polyethylene
terephtalate).
ClearPET bottlesare filledwithwaterandexposedtosunlightforsix hours.The UV A radiation
inthe sunlightkillsinfectiousgermslike,viruses,bacteriaandparasites.The methodalsoworks
at lowair and watertemperatures.

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Figure 4: SODIS method of water purificationxiii
8. LIFE STRAW METHOD
This fairly recent and especially simple method was invented by a
Dane,VestergaardFrandsen,whosells the process through a Swiss
companyof the same name with11 continental or regional entities.
It comprises sucking water through a straw, not a real one, but
rather a small plastic tube 3 cm in diameter and 25 cm long
containingdisinfectantfilters,especially active charcoal and iodine
product based (the latter now to be reduced, given the taste it
sometimes gives to water).
This device, which costs some €3 (in quantity, sometimes more)
should be able to filter 700 to 1,000 litres of water.
The company whichspecialisesinproductsforemergencysituations
or for preventing certain illnesses has also perfected the so-called
“LifestrawFamily”adevice toextendthe principle touse bya whole
family and able to filter 15,000 to 18,000 litres of water.
Advantages - Simplicity, very easy maintenance (simply by blowing into the device to avoid
clogging);Veryhandy whentravellingor when a water treatmentsystem fails; Claimed almost
complete elimination of bacteria and protozoan parasites; No power required; Reduced
turbidity (murky water can be used) by filtering particles down to 0.2 microns
Disadvantages - A product better suited to emergency or temporary situations.; Low cost, but
not easily available
Figure 5: children using
lifestraw

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9. MODERN WATER PURIFIERS
Many companies have come up with modern water purifiers which use techniques such as UV
radiation,Reverse osmosis,activatedcarbonfilteretc.The product can be installed at home for
purifying the fresh water obtained from municipal or ground water supplies.
Advantages – easy to use; water free from all pathogens
Disadvantages – costly, requires expertise maintenance
i https://en.wikipedia.org/wiki/Fresh_water#Definitions
ii Glossary of meteorology.American Meteorologicalsociety. June2000. Archived fromthe original on June, 2011. Retrived on 3 rd July, 2015
iii Fish keeping glossary. Practical fishkeeping. Archived from the original on May, 2006. Retrived on 3rd July, 2018
iv Bureau of Indian Standards, IS 10500: 2012. Drinking water –specification, 2nd edition, New Delhi, May, 2012
v Ann C. Grandjean(August, 2004). Waterrequirements,impinging factors and recommended intakes. WorldHealthOrganization. pp. 25 –34.
vi https://wikiwater.fr/e17-simple-water-treatment-methods#outil_sommaire_1
vii http://www.ihatepsm.com/blog/domestic-or-household-purification-water
viii https://en.wikipedia.org/wiki/Biosand_filter
ix Elliott, M., Stauber, C., Koksal, F., DiGiano, F., and M. Sobsey (2008). Reduction ofE. coli, echovirus type 12 and bacterio phages in an
intermittently operated 2 household-scale slow sand filter.Water Research, Volume 42, Issues 10-11
x "CAWST Biosand Filter Manual 2008" (PDF).
xi https://www.pinterest.ca/pin/282178732877824071/
xii https://www.etsy.com/listing/235481860/stoneware-water-filtration-crock-caspian
xiii https://www.superiorideas.org/projects/sodis