The document discusses methods of water purification on both large and small scales. On a large scale, purification involves storage, filtration using slow sand or rapid sand filters, and disinfection through boiling, chemicals like bleaching powder and chlorine, or filtration. On a small scale, common methods are boiling, sunlight exposure, and chlorination using household bleach. In Pokhara, the main method used by the water corporation is chemical treatment using bleaching powder at the water supply centers.

1. Water purification
Slides prepared by:
Samrat Gurung (Bachelor In Public Health)
Roll no-28
Venue: LA Grandee International College,
Pokhara

2. Water purification
 Water purification is the process of removing undesirable
chemicals, biological contaminants, suspended solids and
gases from contaminated water.
 The goal is to produce water fit for a specific purpose.
 Most water is disinfected for human consumption , but water
purification may be designed for a variety of other purposes
including fulfilling the requirements of medical,
pharmacological, chemical and industrial applications.

3.  Purification of water may reduce the concentration of
particulate matter including suspended particles, parasites,
bacteria, algae, viruses, fungi as well as reducing the amount
of a range of dissolved and particulate material derived from
the surfaces that come from runoff due to rain.
 The purification of water can be categorized into two types:
1. Purification of water on large scale
2. Purification of water on small scale

4.  Storage of water
o physical
o chemical
o biological
 Filtration of water
o slow sand(biological) filters
o rapid sand(mechanical) filters
 Disinfection of water
1. Purification of water on the large
scale-

5. Mainly three methods are used:
 Boiling
 Chemical disinfection
o Bleaching powder
o Chlorine solution
o Chlorine tablets
o Iodine
o Potassium permagnate
 Filtration
2.Purification of water on small scale-

6. 1.Purification on the large
scale-
Storage
 Water is drawn out from the source and impounded in
natural or artificial reservoir.
 Storage provide reserve of the water from which further
pollution is excluded and it may look at in the three points
as:
o Physical: By the mere storage the quality of the water
improves. About 90% of the suspended impurities settle
down in 24 hours by gravity. It allows penetration of light and
reduce the work of filters.

7. o Biological: a tremendous drop takes place in bacterial
count during storage due to antibiosis and oxidation. The
pathogenic organism gradually die out.
o Chemical: certain chemical changes takes place during
storage. The aerobic bacteria oxidize the organic matter
present in the water with the aid of dissolved oxygen.

8. Filtration
 It is the oldest and the universal method of purification . And also
the second stage in the purification of water.
 The filtration reduces the bacterial content from 98-99% and
colour to colourless.
 There are two types of filtration.
o Slow sand filtration(biological filter)
o Rapid sand filter(mechanical filter)

9. 1.Slow sand filtration
 They are cheap and easy to design and occupy less space.
During the 19th century its use spread throughout the world.
 They contain the concrete made basin, which contains the
selected graded sand supported on stones. The contents are-
supernatent water head, sand bed, drainage system and
simple control valve.

11. Advantage of slow sand
filtration-
 Simple to construct and operate
 The cost of the construction is cheaper than that of rapid
sand filters.
 The physical, chemical and bacteriological quality of the
filter is very high.
 It will reduce the bacterical count by 99.99 percent and
E.coli by 99.9%.

12. 2..Rapid sand filters
(mechanical filters)
 In the 1885 the first rapid sand filters were installed in the
USA. Since that time, it gained considerable popularity even
in developing countries.
 It is of two types as gravity type and pressure type. Both are
in use.
 The step involve in the purification of water by rapid sand
filter are:cogulation, rapid mixing, flocculation,
sedimentation and filteration.

14. Advantage of rapid sand
filtration-
 It can deal with raw water directly. No preliminary storage is
required.
 The filter bed occupy less space.
 The initial cost is high but becomes cost effective in nature.
 Filtration is rapid, 40 to 50 times that of slow sand filters.
 The washing of the filter is easy.
 There is more flexibility in operation.

15. Mainly three methods are used:
 Boiling
 Chemical disinfection
o Bleaching powder
o Chlorine solution
o Chlorine tablets
o Iodine
o Potassium permagnate
 Filtration
Purification of water on small scale

16. Purification of water on
small scale-
Boiling
 Equipment/Skill Required:
– Water container
– Intense heat – fuel (wood, gas, etc)
– Preferably a fuel efficient stove
– Must be able to produce heat
 Process:
– Water should be placed in a container and heated until boiling.
– The water should be allowed to boil for at least 10 minutes.
– Once cooled the water will be ready to use.

17. Advantages of boiling-
– Simple and effective method of purification
– Will kill many waterborne bacteria through the
intense heat
– Uses local available materials
Disadvantages of boiling-
– Can sometimes be difficult, time consuming, and
cost inefficient because of the high volume of fuel
used
– Will not remove mud from ‘murky’ water
– Will not remove suspended or dissolved
compounds

18. Sunlight Exposure
 Equipment/Skill Required:
– Disposable clear plastic bottles (glass bottles should not be used
as they do not let enough sunlight into the water)
– Bright sunlight
 Process:
– Fill a clean bottle, leaving a quarter empty.
– Put the top on and shake the bottle for 20 seconds.
– The bottled should then be left in sunlight
(usually on the roof of your home) for one day
(or two days if the sky is cloudy)
– Drink the water straight from the bottle to avoid
cross-contamination.
– In the rainy season, paint one side of the bottle black.
This will increase the water temperature quicker.
– The painted side should be placed underneath

19. Advantages of sunlight exposure-
– Kills harmful bacteria and pathogens
– Simple, convenient and inexpensive
– If used correctly, the water is as clean as
boiled water
– Will not change the taste of water
Disadvantages of sunlight exposure-
– Will not remove mud from ‘murky’ water
– Need 6-12 hour waiting period

20. Chlorination
Equipment/skill required:
– Household bleach
– Water vessel
– Stirrer
– Clearest water possible
Process:
– Boil the water for 5 minutes
– Add the bleach to water.
– Stir thoroughly.
– Let it stand for at least 30 minutes.

21. Advantages of chlorination-
– Easy to use method of chemical purification of
water
– Effective at killing bacteria and viruses
– Inexpensive
Disadvantages of chlorination-
– Not effective at killing all parasites.
– Complex compounds can form with organic
material which over time can be hazardous to
health.
– It is best to use the water in a shorter period of
time and store it in a plastic container in a cool
and shaded place.

22. Water purification in
pokhara-
■ According to Dineshwor Yadav, engineer of
Nepal water supply cooperation in Pokhara
, the corporation supplies 450 millions
liters of water to the customers in the
pokhara city daily.
■ And the main filtration method applied is
the chemical treating(bleaching-powder
treatment).

23. Water treatment by the help of
bleaching powder in supply
center of Pokhara