A Complete Civil Engineering Study Solutions: Examination Of Water (Water Analysis)

Examination Of Water (Water Analysis):

The process of finding out the quality of water is known as Water Analysis.

It consists of:

i. Sampling Of Water

ii. Physical Examination

iii. Chemical Examination

iv. Bacteriological Examination

Sampling Of Water:

As the quality of water changes on daily or seasonal basis, it's important to sample it to analyse it over along period of time.

Samples are collected in sterilized bottles having stoppers. The sterilization is done by heating the bottles or by mixing them with concentrated nitric acid or sulfuric acid. All these acids should be completely removed by washing with sterilized water.

The water or bottle should not be touched at the time of filling.The date, time,place & number should be put down on the bottle. The nature of supply should also be mentioned on the bottle as whether it's collected from well, stream, filter etc.

Both the raw water from the source & the purified water are examined to find out the actual condition of water before & after treatment. This decides the degree of treatment required & whether the treated water being supplied to the consumers from day to day is of the specified standard laid down by the Public Health Department.

Physical Examination:

In this sub menu the physical properties of water is examined.They are as:

Temperature: Desirable range of temperature for public water supply is seldom below 40° F to 50° F.
Color : The color of potable water is 10-20 ppm on platinum cobalt scale. The shade of color present in water is determined by comparing it with a standard unit consisting of 1 mg of platinum per liter of water. Basically color is imparted to water due to decaying of vegetable organic substances dissolved in it.
Turbidity: It's the measure of muddiness of water. For drinking water a turbidity of less than 10 ppm is desirable. The optimum is 5 ppm.
Odour: The odour in water is due to organic substances, vegetable matter, microscopic organism of gases which are still undergoing decomposition. The measurement of odour intensity is made by diluting the sample with odour free water to the threshold value. The dilution ratio is generally 1:4 which will be obtained when 50 ml water sample is diluted & is made 200 ml.It should be 1 & should never exceed 3 for public supplies.
Taste: Taste in water may be due to dead or alive microorganisms, mineral substances like sodium chloride, iron compounds, carbonate & sulphates & other oily matter especially after chlorination.

Chemical Examination:

In this sub menu the chemical properties of water is examined.They are as:

Total Solids: The impurities of water in the suspended, colloidal & dissolved forms are termed as total solids in water. The quality of solids present in water can be found out by eavporating a sample of water & then weighing the dry residue left. To find the suspended solids, the water sample is filtered and the residue left on filter paper is weighed. The difference between total solids & suspended solids will give the dissolved solids. Total solid in domestic water should not be mare than 500 ppm, higher amount of 1500 ppm is also permitted but it leads to some psychological effects on human body.
Hardness: It is property of water which prevents the lathering of soap. It is due to presence of carbonates, bicarbonates, sulphates, chlorides & nitrates of calcium & magnesium. It leads to scale formation in the boilers & consumption of large amount of soap for domestic use. It's measured in mg/l or ppm. The water is said to be soft if it's hardness is upto 50 ppm, moderately soft if between 50 ppm to 100 ppm, slightly hard if 100 ppm to 150 ppm, moderately hard if 150 ppm to 200 ppm & very hard if more than 200 ppm.
pH Value: It is the logarithm to the base 10 of reciprocal of hydrogen ion concentration expressed in gm/l. The pH value of domestic water should range between 6.5 to 8.
Chlorides: Chlorides are usually present in water in the form of sodium chloride (NaCl) & may have access to water due to pollution from sea water, industrial & domestic wastes etc. It imparts salty taste in water. It should not exceed 250 gm/l.
Chlorine: It is present in the treated water resulting from disinfection with chlorine. It's limited from 0.05 to 0.2 ppm in water to kill the disease borne bacteria.
Iron & Manganese: It causes discoloration in cloths when washed. It's restricted to 0.3 ppm in potable water.
Organic Matter: It is produced by decaying vegetable or plant matter & waste products from animal & human beings.
Fluorides: A minimum amount of fluorides is desirable in a potable water in prevent dental cavities & the maximum amount is limited by the need for the prevention of fluorosis, a defect of enamel of the teeth.

Bacteriological Examination:

It is a safer criterian for determining the fitness of water for drinking than a chemical analysis & consequently is of prime importance to the water works engineer.
There are two standard tests performed:

i. Total Count Of Bacterias:

In this method total number of bacterias present in water in ml of water is counted. 1 ml of water sample is diluted in 99 ml of sterilized water. Then 1 ml of diluted water sample is added to 10 ml of agar. The mixture is kept in incubator at 37 degree Celsius for 24 hrs. Then colonies of bacterias are counted by means of microscope. Then the product of total number of colonies & the dilution factor will indicate the total number of bacterias per ml of undiluted water sample.

ii. B-Coli Test:

The presence of B-Coli indicates that the excreta of men & animals have mixed with with water & haven't yet been destroyed.

The examination for bacteria of coli-aerogenes group consists:

Presumptive Test
Confirmed Test
Completed Test

Presumptive Test:

In this amount of diluted water sample is incubated in a standard fermentation tube containing lactose broth for 24 or 48 hrs at 37 degree celcius. If there is evolution of gas in 24 hrs, it means the test is positive & water water is not safe & vice versa.

Confirmed Test:

In this, a small material from the positive presumptive test is transferred to the second fermentation tube containing brilliant green lactose as a liquid confirmatory medium. Contents are incubated for 48 hrs 37 degree Celsius, Absence of gas means test is negative & water is safe.

Completed Test:

It is performed to show whether or not the gas forming organisms are Gram negative, non-spore-forming bacilli.

Examination Of Water (Water Analysis)