3. The Three-Step Docking Procedure versus the Hybrid Procedure
3.6. Results And Discussion
These may be classified as physical, chemical and micro-biological standards, as described below.
PHYSICAL STANDARDS
Wholesome water should be odorless, tasteless and clear without any turbidity.
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CHAPTER 6: Physical Environment: Water
Color
A large collection of water may be apparent as pale blue or pale green, otherwise water is colorless. However, it may be reddish when iron salts are present in it. A dilute solution of K2CrO7 and cobalt sulfate in the tintometre is used to measure the color. There is a standard series or colored tubes. The color of good water is 0.5 on Hazen scale. It should not be more than 5 units as per the platinum cobalt scale.
Odors
They are imparted by algae and organic and mineral matter that reaches water through seepage or from industries. Algae give a fishy or putrescent odor on decomposition. Tar, peat and gases impart their typical smells. No disagreeable smell is permissible in portable water.
Taste
A pleasant taste is due mainly to dissolved O2 and CO2. That is why boiled, distilled or rainwater has a flat or insipid taste. The taste can be regained by shaking. Well water may sometimes be brackish in taste.
Reaction
Sour taste is due to acids (excess of CO2) and bitter taste is due to alkalies (such as ammonia) from decaying organic matter like dead animals, leaves, rotten wood and dead marsh plants. pH should be 7 to 8.5.
Turbidity
It is due to fine particles of mud, sand, slime, clay, loam, and organic matter and a large variety of aqueous microorganisms including plantation suspended in water.
They settle down by storage or on adding alum. Turbidity can be measured by Jackson-Candle turbidimeter. The permissible limit is up to 5 units.
Radiological Quality
Increasing pollution of water sources10 with radioactive wastes from nuclear reactors has become a problem during recent years. Another source is the radioactive debris from nuclear fall ou ts. This debris, usually from a nuclear detonation, is deposited on the earth after having been blown by the winds. International standards for the upper limit of radioactivity in water are as follows:
Gross alpha activity—3 picocurie/l Gross beta activity—30 picocurie/l.
CHEMICAL STANDARDS
The WHO had laid down water standards under three categories.8
Toxic Substances
These are lead, selenium, arsenic, cyanide and mercury.
Substances that may Affect Health
• Fluorine: It should be present in a concentration of 0.5 to 0.8 mg/l to prevent caries. Concentration less than 0.5 mg/l is associated with caries in the population. Excess fluoride (more than 1.5 parts per million) causes chalky discoloration of teeth, seen first on incisors as transverse patches. Levels above 3.5 PPM may be associated with skeletal fluorosis. High fluoride content has been found in Punjab (up to 44 PPM and beyond), Andhra Pradesh, Tamil Nadu, Kerala and Junagadh district of Gujarat.
• Nitrates: Some water samples may be too rich in nitrates. Amounts in excess of 45 mg/l (as NO3) may cause methaemoglobinemia in infants. No harmful effects are seen in adults.
• Polynuclear aromatic hydrocarbons (PAH): These may be carcinogenic. They should not be present in water in excess of 0.2 mg per liter.
Substances that may Affect Water Acceptability
These include—iron, calcium, copper, zinc, etc. Their presence affects water acceptability due to changes in color, taste, etc.
The levels of various chemical substances permissible in drinking water have been given by WHO8 as “highest permissible levels” and by Indian Standards Institute9a as
“desirable upper limit”. These are shown in Table 6.1.
Besides the above, other BIS standard for drinking water (upper limit) are: Color (10 Hazen units), Turbi-dity (10 NTU), pH (6.5 to 8.5).
It may be mentioned here that tube-well water in some parts of Delhi has excessive levels of iron and chlorides. It is also too hard in some areas.
Hardness of Water
Water is said to be hard when it destroys soap because of the dissolved salts. These salts are bicarbonates, sul-fates and chlorides of calcium and magnesium. The hardness due to the presence of bicarbonates was earlier labelled as temporary hardness as compared to permanent hardness due to other salts. These terms are no longer used now. Hardness is expressed as milliequivalents per liter of the hardness producing ion.
Thus a sample of water having 50 mg of calcium carbonate per liter would have 1 mEq/L of hardness.8 Water can be categorized as soft or hard as follows:
mEq/L
Soft 0-0.9
Moderately hard 1-2.9
Hard 3-5.9
Very hard 6 and above
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PART II: Epidemiological Triad TABLE 6.1: Chemical standards for water
WHO BIS
• Toxic substances
Lead (as Pb) 0.05 0.1
Selenium (as Se) 0.001 0.01
Arsenic (as As) 0.05 0.05
Cadmium (as Cd) 0.005 0.01
Cyanide (as Cn) 0.05 0.05
Mercury (as Hg) 0.001 0.001
• Substances that may affect health
Fluoride (as F) 0.6–1.2
Nitrates (as NO3) 45
• Substances that may affect acceptability
Iron (as Fe) 0.1 0.3
Calcium (as Ca) 75 75
Copper (as Cu) 0.05 0.05
Zinc (as (Zn) 5 5
Manganese (as Mn) 0.05 0.1
Magnesium (as Mg) 30 30
Total dissolved 500 500
solids
Chloride (as Cl) 200 250
Sulfate (as SO4) 200 150
Phenolic (as C6H5OH) 0.001 0.001 substances
Total hardness (as CaCO3) 100 300
Mineral oil 0.01
Residual free chlorine 0.02
NB—All values are in mg/liter. BIS = Bureau of Indian Standards
Too soft water is insipid in taste. Drinking water should be preferably moderately hard.
Hardness is objectionable for the following reasons:
• Hard water precipitates soap forming curds. Hardness causes wastage of soap and difficulty in laundering, bathing and hair washing.
• Hard water affects the durability of textiles.
• Hard water causes encrustation in boilers and utensils which might crack on sudden heating. Encrusted utensils require more fuel for heating. Hard water also causes scaling, encrusting, occlusion and bursting of water pipes.
• Hard water is unsuitable for certain industries.
There is no conclusive evidence that hardness affects health. Some people get digestive upsets when they are not used to hard water. On the other hand, coronary artery diseases has been found to be more common in areas with soft water supply. This has been attributed to magnesium deficiency.11
MICROBIOLOGICAL STANDARDS
Ideally, drinking water should not contain any micro-organism at all. This ideal is unattainable. Natural waters contain various types of bacteria that may be saprophytes, coliforms (typical, atypical and intermediate atypical coliforms, IAC) and pathogens for cholera, typhoid, dysentery, etc. The main aim of testing for water quality is to look for the presence of coliform
bacteria in water to know whether water is being polluted by human excreta which may contain pathogens. Most authorities now insist that water should be free from all sorts of E.coli as well as fecal streptococci. The WHO has recommended the following criteria of safety for large water supplies:
• No sample should have E.coli in 100 ml.
• No sample should have more than 3 coliforms per 100 ml.
• Not more than 5 percent samples throughout the year should have coliforms in 100 ml.
• No two consecutive samples should have coliform organisms in 100 ml.
The above standards may have to be relaxed in case of small water supplies from wells, etc. In such cases isolated samples should not have more than 10 coliforms per 100 ml. Persistent presence of coliforms, especially of E.coli, would indicate that the water is unsafe for drinking.
While detailed microbiological techniques are to be found in appropriate textbooks, a brief description of the method used for surveillance of water quality is given here. These methods are of four types: presumptive coli-form test, colony count, test for fecal streptococci and Clostridium perfringens and tests for pathogens.
Presumptive Coliform Count (Multiple Tube Technique)
It is done on lactose bile salt medium (MacConkey’s broth), which is a selective medium for coliform bacteria which produce acid and gas. Acid is indicated by the medium turning red. Gas gets collected in the Durham’s tube.
Method: Sterilize 16 tubes containing single or double strength MacConkey’s fluid medium. Add different quantities of water to be tested as follows:
• 50 ml water to 50 ml double strength medium in one tube.
• 10 ml water to 10 ml double strength medium in each of 5 tubes.
• 1 ml water to 5 ml single strength medium in each of 5 tubes.
• 0.1 ml water to 5 ml single strength medium in each of 5 tubes.
• Incubate for 48 hours and read the result.
The probable number of coliform bacilli per 100 ml of water is found by referring to McCrady’s table. It is called presumptive count because the actual number of organisms in the sample of water is not counted. It is presumed that each of the tubes in the test showing fermentation contains coliform organisms.
Further confirmation of the type of coliform organisms is done by the Eijkman’s test. In this test the typical fecal Escherichia coli are differentiated from nonfecal coliforms by incubating the tubes at two different temperatures, viz., 37°C and 44°C. The E. coli grow at 44°C while the other coliforms do not.
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CHAPTER 6: Physical Environment: Water
Colony Count
The aim here is to have an estimate of the general microbiological quality of water. The standard count involves inoculating nutrient agar plates with 1 ml water and inoculating them at two different temperatures—
22°C for 72 hours and 37°C for 48 hours. The number of colonies is then counted. The growth at 22°C indicates the presence of saprophytes. The following guidelines for safe water are used for interpretation:
Disinfected water—Plate count 0 at 37°C and upto 20 at 22°C.
Undisinfected water—Plate count up to 10 at 37°C and not more than 100 at 22°C.
A high total count at 22°C has no value. However, sudden changes from low to high may indicate pollution.
Uncontainated well water may have a total count of 100 to 200 per ml. Surface waters have high count, especially after rains, while groundwaters usually have a low count.