Water quality describes the condition of the water, including chemical, physical, and biological characteristics, usually concerning its suitability for a particular purpose such as drinking.

1. Water quality and analysis of
drinking water quality
Presented by
A.R. Deborah (BP211501)
I M.Sc. Applied Microbiology
Sacred Heart College (A)
Tirupattur.

2. WATER QUALITY
• Globally, 2 billion people using a drinking water source
contaminated with faeces. Microbial contamination of drinking
water is highly risk to drink contaminated water.
• Most important chemical risks in drinking water from fluoride
or nitrate, emerging contaminants such as pharmaceuticals,
pesticides and microplastics generate public concern.
• Drinking water must be visually clear and colourless, and
without disagreeable taste and odour.

3. • Water quality is measured by several factors such as the
concentration of dissolved oxygen, bacteria levels, the salinity
and turbidity.
• Poor water quality has a direct impact on aquatic wildlife like
fish and plants.
• Excess of nutrients, sediment, road salt, and other
contaminants can reduce the variety of organisms living in the
water.
• Waterborne diseases like typhoid fever, cholera, diarrheal
diseases, poliomyelitis, hepatitis A & E.

4. WATER QUALITY PARAMETERS
• Water quality is a measure of suitability of water for a particular use
based on selected physical, chemical and biological characteristics.
• Physical properties
• Temperature
• Colour
• Odor
• Turbidity
• Electrical conductivity
• Temperature of water
Essential for all environmental studies.
Controls many ecological processes including chemical reactions.
Measured using thermometer
It ranges from 0 to 100 degree Celsius.
The temperature of the surface water is influenced by atmospheric condition.

5. • Colour of water
The colour of water is due to the suspended particles and organic matter.
Ranges from light to dark brown
Brownish colour in water comes due to the presence of iron
Greenish colour in the pond water is due to the presence of organic substance
including algae.
• Odor
Pure water is odorless when water dissolve other substance the odor is
determined by them
Mostly decade organic substance is gives fouling smell.
Inorganic substance gives earthy smell.
• Turbidity
 Muddiness in water comes due to suspended particles from clay slit and
organic matter.
Controls the transparency of water Transparency is measured using Secchi disc
Water turbidity is measured using nephelometer.

7. • Electrical conductivity
Ability of a substance to conduct electrical current. It is measured using EC meters.
Pure water is less conductive
• Chemical properties
• pH
• Total dissolved solids major ions
• Minor or trace elements
• Salinity
• Alkalinity
• pH of water
Water is said to be acidic less than 7 or alkaline depending on the relative
concentration of hydrogen ion from the neutral value which is 7
It ranges from 0 to 14 measured using pH meter
• Total dissolved solids
Concentration of non volatile substance present in molecular state
Total of all ions present in water is expressed in PPM or mg per liter
Quality of water total dissolved solids PPM
 < 10000 Fresh water ,1000 -10000 Brackish water
10000-100000 Saline ,>100000 Hypersaline or brine

8. • Trace elements
Play a significant role in the use of water some Essential elements for health
and growth
• Salinity
Salinity of water comes due to Sodium and chloride
The water contains 35000 PPM or mg per liter of dissolved solids
• Alkalinity
Alkalinity of water combined effect of bio carbonates and carbonates with
calcium ion carbonate will be noticeable for water having pH more than 8.2
• Biological properties
• Dissolved oxygen (DO)
• Biochemical oxygen demand (BOD)
• Chemical oxygen demand (COD)

9. • Dissolved Oxygen
It is related to the solubility of air in water at 0 degree Celsius
Solubility of oxygen in water decreases with high temperature
Important property for aquatic organisms
If dissolved oxygen depletes it will be difficult to many aquatic organisms for
their survival
• Biochemical oxygen demand
It is a measure of biodegradable material
It is determined by incubating a water sample and measuring the decrease
of dissolved oxygen as bacteria decompose these materials.
• Chemical oxygen demand
It is determined by the oxidation of water with dichromate

10. ANALYSIS OF DRINKING WATER QUALITY
The following tests are generally done for routine
coliform analysis of water
 Plate count
 MPN test
 Membrane filtration method

11.  Plate Count
 The most frequently used method of measuring bacterial populations is the
Plate count.
 A Plate count is done by either the Pour plate method or the Spread plate
method.
 In the Spread plate method, a volume (0.1 ml) of an appropriately diluted
culture is spread over the surface of an agar plate using a sterile glass spreader.
 In the Pour plate method, a known volume (1 ml) of culture is pipetted into a
sterile Petriplate. The usual practice, which is most valid statistically, is to
count colonies only on plates that have between 30 and 300 colonies. Less than
30 colonies is represented as Too Least to Count (TLTC). More than 300
colonies is represented as Too Numerous to Count (TNTC)
 Advantage - It measures the number of viable cells.
 Disadvantage - It takes some time, usually 24 hours or more, for visible
colonies to form. This can be a serious problem in some applications, such as
quality control of milk, when it is not possible to hold a particular lot for this
length of time.

12.  Most Probable Number Test
 Most Probable Number (MPN) is a method used to estimate the
concentration of viable microorganisms in a water sample.
 MPN is most commonly applied for quality testing of water i.e to
ensure whether the water is safe or not.
The most probable number (MPN) is a statistical method used to
estimate the viable numbers of bacteria in a sample by inoculating
broth in 10-fold dilutions and is based on the principle of extinction
dilution.
Coliform bacterial densities can be determined by either Multiple
tube fermentation technique (MPN Test) by Membrane filter (MF)
procedure. The Multiple tube fermentation technique providing the
Most portable number (MPN) is an Indirect count technique relying
on statistical interpretation of growth. The test was conducted in
three steps such as Presumptive test, Confirmatory test and Complete
test.

13. Presumptive test
Distribute 10 ml Single strength lactose broth (SSLB) each to 10 test tubes and
Double distilled strength Lactose broth (DSLB) to 5 test tubes.
Add the Durham's tube in inverted position and sterile them at a time.
After autoclave, Inoculate the 0.1 ml of water sample to each 5 tubes of SSLB, 1 ml
of water sample to each 5 tubes of SSLB tubes and 10 ml of water sample in 5
tubes of DSLB correspondingly.
Incubate the tubes at 37 °C and examine the gas formation in Durham’s tubes at 24
hours (positive test) or not 48 hours (doubt full tests) proceed to confirmed.
Compare the number of tubes giving positive reaction to a standard chart and
record the number of bacteria present in it.

14. Confirmative test
Take a loopful culture from the Lactose broth tube from the highest
dilution that still showed positive test and streaks it on EMB agar
plate.
Incubate the plates at 37 °C for 24 hours.
Observe for the typical Escherichia coli colonies showing greenish
metallic sheen.
Complete test
Pick up a suspicious colony (Escherichia coli) from EMB agar plate,
make a smear and conduct Gram staining.

15.  Membrane Filter Technique
 The number of bacteria in aquatic samples is frequently
determined from direct counts after the bacteria have been
trapped on special Membrane filters.
 In the Membrane filter technique, at least 100 ml of water are
passed through a thin Membrane filter whose pores are too small
to allow bacteria to pass. Thus, the bacteria are filtered out and
retained on the surface of the filter. This filter is then transferred
to a Petridish containing a pad soaked in liquid nutrient medium,
where colonies arise from the bacteria on the filter’s surface.
 Membrane filter technique is applied frequently to detection and
enumeration of coliform bacteria, which are indicators of fecal
contamination of food or water.

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