for those who are in need of notes.

1. PHARMACOEPIDEMIOLOGY
AND ENVIRONMENTAL
HEALTH
2.4 Water
purification

2. WATER PURIFICATION
• Water purification is the process of removing undesirable chemicals,
biological contaminants and suspended solids from contaminated
water. The goal of this process is to produce water fit for a specific
purpose. Most water is disinfected for human consumption but water
purification may also be designed for a variety of other purposes,
including meeting the requirements of medical, pharmacological,
chemical and industrial applications.
• The purification process of water may reduce the concentration of
particulate matter including suspended particles, parasites, bacteria,
algae, viruses, fungi; and a range of dissolved and particulate
material derived from the surfaces that water may have made
contact with after falling as rain.

3. METHODS OF WATER
PURIFICATION
• There are two types of water purification methods
namely:
1) Small scale water purification method
2) Large scale water purification method

4. SMALL SCALE WATER
PURIFICATION METHOD
• At small scale or domestic level water can be purified by
the following methods:
1) Boiling
2) Filtration through muslin cloth
3) Chemical treatment

5. BOILING
• Boiling is the oldest and satisfactory method of purification
of water on small scale. Boiling for 5 to 10 minutes kills
bacteria, spores, cysts and ova of intestinal parasites. It also
removes hardness of water and soft water is produced.
• Boiling is an excellent method of purification of water
provided. Boiling is done in a neat and clean vessel and
after boiling it is stored in clean covered container.
Preferably water should be boiled in the same container in
which it is to be stored.

6. FILTRATION THROUGH MUSLIN
CLOTH
• Muslin cloth acts as a coarse filter which can remove the
suspended materials. So water filtered through muslin is not
fit for drinking purposes though it can be used for other
household purposes like bathing, washing the clothes etc.

7. CHEMICAL TREATMENT
• Various types of chemicals are used for purifying water such
as:
A) Bleaching powder (Chlorinated Lime):
➢ Roughly speaking 2.5 gm of a good quality of bleaching
powder could be required to disinfect 1000 liters of water.
Bleaching powder will not directly purify the turbid and
polluted water. Therefore such water should first be treated
with preliminary filtration and then subjected to chlorination.

8. B) Chlorine tablet:
➢ These tablets are good for disinfecting small quantities of
water. They are available in different strengths for
disinfecting various quantities of water. One tablet of 500
mg is sufficient for disinfecting 20 liters of water. These are
available in the market under various trade names e.g.
halazone tablets manufactured by the Boots company.
C) Quick lime (Calcium Oxide):
➢ Some people prefer to use dry slaked lime than ordinary
lime. About 360 mg of slaked lime will disinfect 4.5 liters of
water. It is cheap, easily available and quite effective.
➢ Therefore it is recommended for disinfecting wells and tanks
in cholera outbreak. Disadvantage of quick lime is that
large doses of it are required for disinfection of water i.e. 20
times than that of bleaching powder.

9. DISINFECTION OF WELL
• You can disinfect your well with household chlorine bleach.
Use fresh chlorine bleach to ensure an effective disinfection
of the well. Chlorine can evaporate and lose half of its
strength in 6 months. Don't use scented bleach, to avoid
adding extra chemicals to your water.
• Potassium permanganate is used for disinfecting wells. Its
dose is 0.5 parts per million (0.5 ppm). It is not suitable for
disinfecting large volume of water. Its disadvantages are
that it alters the taste, smell and color of water thus treated.
Moreover this method is not considered dependable
therefore no longer used for disinfecting the water.

10. LARGE SCALE WATER
PURIFICATION METHOD
• Following are the large scale water purification methods:
1) Slow sand filtration
2) Rapid sand filtration

11. SLOW SAND FILTRATION
• Slow sand filtration is a type of centralized or semi-centralized
water purification system. A well-designed and properly
maintained slow sand filter (SSF) effectively removes turbidity
and pathogenic organisms through various biological,
physical and chemical processes in a single treatment step.
Only under the prevalence of a significantly high degree of
turbidity or algae-contamination, pre-treatment measures
(e.g. sedimentation) become necessary.
• Hence, slow sand filtration is a promising filtration method for
small to medium-sized, rural communities with a fairly good
quality of the initial surface water source. As stated by the
WHO, slow sand filtration provides a simple but highly effective
and considerably cheap tool that can contribute to a
sustainable water management system.

12. • Process of slow sand
filtration:
➢ The basic principle of the process is very
simple. Contaminated freshwater flows
through a layer of sand, where it not only gets
physically filtered but biologically treated.
Hereby, both sediments and pathogens are
removed. This process is based on the ability
of organisms to remove pathogens.
Fig: Slow Sand Filtration

13. ILLUSTRATION OF A SLOW SAND FILTER WITH A REGULATING VALVE AND A SUBSEQUENT
RESERVOIR
➢ As the process itself, the basic
structure is very elementary.
Essentially, only the filter chamber, a
type of reservoir and pipes are
required. The filter chamber can
either be constructed as an open or
as a closed box. Depending on
climatic and other factors, the one
or the other is more reasonable (e.g.
cold climate requires a closed box
since low temperatures decrease
the performance of the process).
Fig: Slow Sand Filtration with regulating valve and a subsequent reservoir

14. RAPID SAND FILTRATION
• Rapid sand filtration is a purely physical drinking water
purification method. Rapid sand filters (RSF) provide rapid and
efficient removal of relatively large suspended particles. Two
types of RSF are typically used: rapid gravity and rapid
pressure sand filters. For the provision of safe drinking water,
RSFs require adequate pre-treatment (usually coagulation-
flocculation) and post-treatment (usually disinfection with
chlorine). Both construction and operation is cost-intensive.
• It is a relatively sophisticated process usually requiring power-
operated pumps, regular backwashing or cleaning, and flow
control of the filter outlet. Rapid sand filtration is common in
developed countries for the treatment of large quantities of
water where land is a strongly limiting factor, and where
material, skilled labor, and continuous energy supply are
available.

15. PARTS OF RAPID SAND
FLOW
➢ The section of rapid sand filter consists of
the following:
a) Enclosure tank
b) Filter media
c) Base material
d) Under drainage system
e) Appurtenances
Fig: Rapid Sand Filtration

16. PURIFIED WATER
• Purified water is water that has been mechanically filtered or
processed to remove impurities and make it suitable for use.
Distilled water was, formerly, the most common form of
purified water, but, in recent years, water is more frequently
purified by other processes.
• Combinations of a number of these processes have come into
use to produce ultrapure water of such high purity that its
trace contaminants are measured in parts per billion (ppb) or
parts per trillion (ppt).

17. USES OF PURIFIED WATER
• Purified water is suitable for many applications, including
autoclaves, laboratory testing, laser cutting, and automotive use.
Purification removes contaminants that may interfere with
processes, or leave residues on evaporation.
• Although water is generally considered to be a good electrical
conductor, for example, domestic electrical systems are
considered particularly hazardous to people if they may be in
contact with wet surfaces, pure water is a poor conductor.
• Purified water is used in the pharmaceutical industry. Water of this
grade is widely used as a raw material, ingredient, and solvent in
the processing, formulation, and manufacture of pharmaceutical
products, active pharmaceutical ingredients and analytical
reagents.
• Purified water is also used in the commercial beverage industry as
the primary ingredient of any given trademarked bottling formula,
in order to maintain critical consistency of taste, clarity, and color.
This guarantees the consumer reliably safe and satisfying drinking.

18. DISTILLED WATER
• Distilled water is water that has been boiled into vapor and
condensed back into liquid in a separate container. Impurities
in the original water that do not boil below or near the boiling
point of water remain in the original container.
• Distilled water is safe to drink. But you'll probably find it flat or
bland. That's because it's stripped of important minerals like
calcium, sodium, and magnesium that give tap water its
familiar flavor. What's left is just hydrogen and oxygen.

19. USES OF DISTILLED WATER
• Drinking Water
• Cooking & Baking
• Crystal Clear Ice
• Baby Formula
• Water for Plants & Seeds
• Washing Hair
• Humidors
• Car Batteries and Car Radiators
• Continuous positive airway passage(CPAP) Machines
• Health Care Use
• Cleaning
• Used in aquariums

20. WATER FOR INJECTION
• Water for injection is water of extra high quality without
significant contamination. A sterile version is used for making
solutions that will be given by injection. Before such use other
substances generally must be added to make the solution
more or less isotonic. It can be given by injection into a vein,
muscle, or under the skin. A non-sterile version may be used in
manufacturing with sterilization occurring later in the
production process.
• If it is given by injection into a vein without making it
approximately isotonic, breakdown of red blood cells may
occur. This can then result in kidney problems. Excessive
amount may also result in fluid overload. Water for injection is
generally made by distillation or reverse osmosis.

21. USES OF WATER FOR INJECTION
• It is used to deliver medications or drugs to patients
intravenously.
• It is used as a cleaning agent because of its extensively
purified nature.
• It is used to dissolve or dilute substances or preparations for
parenteral administration.
• It may also be used as an irrigating solution for small wounds or
during minor surgical procedures.

22. SANITARY WELL
• A sanitary well is one that is properly located, well
constructed, and well protected from possible
locations of contamination so as to ensure supply
of safe water.
• Criteria for sanitary wall are as follows:
➢ Location
➢ Lining
➢ Parapet wall
➢ Platform
➢ Drain
➢ Cover
➢ Handpump
➢ Consumer responsibility
➢ Quality
Fig: Sanitary Well