Coupon Accepted Successfully!



  1. Water Requirement
    1. ​For drinking purposes: 2 lit per head / day
    2. Domestic use: 150-200 lit / head / day in urban aeas
    3. In rural areas goal is to provide 40 lit / capita / day
  2. Sources of water supply
    1. Rain
    2. Surface water
      1. ​Impounding Reservoir
      2. Rivers & streams
      3. Tanks, ponds & Lakes
    3. ​Ground water
      1. ​Shallow wells
      2. Deep wells
      3. Springs
      4. Tube wells
  3. Water Pollution
    1. Sources of pollution:
      1. ​Sewage
      2. Industrial & trade waste
      3. Agricultural waste
      4. Physical pollutants
    2. Indicators of Water pollution
      1. Amount of total suspended solids
      2. Biochemical oxygen demand at 20 degree C
      3. Concentration of Chloride, Nitrogen & Phosphate
      4. Absence of dissolved oxygen
  4. ​​Water borne diseases

1. Those caused by presence of an infective agent

a.  Viral

Viral hepatitis A, hepatitis E, poliomyelitis, rotavirus diarrhea in infants

b.  Bacterial

Typhoid & paratyphoid fever, bacillary dysentery, E coli diarrhea, cholera

c.   Protozoal

Amebiasis, giardiasis

d.  Helminthic

Roundworm, threadworm, hydatid disease

e.  Leptospiral

Weil’s disease

2. Those due to presence of aquatic host

a.  Snail


b.  Cyclops

Guinea worm, fish tape worm

 3. Water – related disease can be classified into 4 major categories, as follows:

a.  Water-borne disease

Infections spread through contaminate drinking water eg. Cholera, Typhoid etc.

b.  Water-washed diseases:

Diseases due to the lack of proper sanitation and hygiene eg: scabies, worm infestation

c.   Water-based diseases:

Infections transmitted through an aquatic invertebrate organism eg. Schistosomiasis, guinea worm, paragonimiasis, clonorchiasis etc.

d.  Water – related vector borne disease

Diseases transmitted by insects that depend on water for their propagation e.g malaria, filaria etc.

  1. Safe and wholesome water: Water
    1. defined as water that is
      1. Free from pathogenic agents
      2. Free from harmful chemical substances
      3. Pleasant to taste
      4. Usable for domestic purposes
        % Population with access to safe water in India: 85%
    2. ​Biological water quality standards set out by WHO
      The WHO has set out the following criteria for water quality:
      1. No sample should have E. coli in 100 ml.
      2. No sample should have more than 3 coliforms per 100 ml.
      3. Not more than 5% samples throughout the year should have coliforms in 100 ml.
      4. No two consecutive samples should have coliform organisms in 100 ml.
    3. ​Chemical water quality standards
      The WHO has set out three chemical quality standards:
      1. Toxic substances – The upper permissible levels of lead, selenium, arsenic, cyanide, cadmium, and mercury are 0.01, 0.01, 0.01, 0.07, 0.003, and 0.001 mg / litre in domestic drinking water.
      2. Substances that may affect health
        1. ​Fluorine should be present in a concentration of 0.5 – 0.8 mg/l.
        2. Nitrates should not exceed 45 mg/l.
        3. Polynuclear aromatic hydrocarbons should not exceed 0.2 micrograms per litre.
      3. Substances that may affect water acceptability
        1. Upper permissible limits have been set out for a number of substances like iron, calcium, chloride, sulphate, etc.
        2. Total hardness should not exceed 2 meq/ liter.
        3. Turbidity <5 nephelometric turbidity units.
        4. Chloride: 200mg / L.
        5. Ammonia: Indicator of bacterial , sewage pollution, compromises the disinfection ability by forming nitrites, also causes failure of Mn ion removal from filtration system.
        6. pH: Acidic water <7 pH causes elevated Pb levels & >8 causes chlorination to be ineffective.
        7. hydrogen sulphide : prominent in ground water.
        8. Iron: Ferric ion causes objectionable reddish brown colour.
        9. Manganese: stains sanitary wares; forms coating on pipes.
        10. Radiological aspects:
          • ​​Somatic effects (carcinogenesis): probability of effect rather than severity is a function of dose without a threshold – Stochastic effect.
          • For other effect the severity varies with the dose, a threshold may exist – Non stochastic effect.
    4. ​​​Purification of water
      (4A). Purification of water on a large scale: method of t/t depends upon the nature of raw water & desired standards of water quality. Components:
      1. ​Storage: water is impounded in natural or artificial reservoirs.
        • ​​This natural purification offers many advantages viz:
        1. ​​Physical: About 90% of suspended impurities settle down in 24 hrs by gravity. Water becomes clearer & allows better penetration of light & reduces the work of filters.
        2. Chemical: Aerobic bacteria oxidize the organic matter with the aid of dissolved oxygen which reduces free ammonia & raises the nitrate level.
        3. Biological: tremendous drop occurs in bacterial count ( >90% in first 5-7 days for river water). Optimum recommended period for storage of river water is 10-14 days. Longer period of storage results in growth of algae imparting bad colour & taste to water.
      2. Filtration
        1. Slow sand filter/Biological filter
          1. Slow Sand filter or Biological filters: Elements:
            1. Supernatant raw water
            2. Bed of graded sand
            3. Under drainage system
            4. System of filter control valves
          2. Vital layer:
            1. surface of sand is covered with slimy growth known as Schmutzdecke/ vital/ zoogleal or biological layer.
            2. Formation of vital layer is known as ripening of filter.
          3. Filtration rate lies between 0.1- 0.4 m3 /hour/ per square meter
          4. Removes organic matter, holds back bacteria & oxidizes ammoniacal nitrogen in to nitrate.
          5. Pre treatment by plain sedimentation
            1. ​Water head of 1.0 – 1.5 meters depth
            2. Sand bed (1.25 meters thick) composed of sand particles of 0.15 – 0.35 mm in diameter supported on a layer of fine and coarse gravel
          6. ​Drainage system for the filtered water
            1. ​Filter control valves in the outflow pipe which helps to regulate the outflow of water.
          7. Removes 99.99% of bacteria
          8. Occupies a larger space
          9. Advantages:
            1. simple to construct & operate, cheap to construct.
            2. Physical, chemical & bacteriological quality of water is very high.
        2. ​​Rapid sand filter / Mechanical filter
          1. Water+ alum→ mixing chamber→ flocculation chamber→ sedimentation tank → filter→ chlorine added→ clear water storage→ consumption.
          2. Rate of filtration is 5-15 m3 / m2/ hour.
          3. Effective size of sand particle is 0.4-0.7mm.
          4. Back washing: cleaning of filter.
          5. Treatment by chemical coagulation & sedimentation.
          6. Before the water comes to the filter it is subjected to a process of coagulation with alum.
          7. The filter bed is essentially similar to slow sand filter with two differences:
            1. ​The sand is coarser.
            2. The biological membrane in slow filter is replaced by a layer of alum floc.
          8. ​The rate of filtration in a rapid filter is 4000- 7500 liters per square meter as against 100 – 400 liters in a slow sand filter.
          9. Removes 98-99% bacteria.
          10. Occupies very little space.
          11. Advantages: can deal with raw water directly, filter beds occupy less space, filtration is rapid, washing of filters is easy, more flexibility in operation.
      3. ​​​​Disinfection
        1. Chlorination
          • ​​Chlorine kills pathogenic bacteria but has no effect on certain spores, protozoal cyst, helminthic ova and virus (polio & viral hepatitis)
          • Oxidises iron, manganese and hydrogen sulphide.
          • Destroys odour and taste producing constituents.
          • Control algae & slime organism and aid coagulation.
          • Action of chlorine is due to hypochlorous acid. And acts best at pH 7.
          • Action: H2O + Cl2 → HCl + HOCl Disinfectant activity
                         HOCl [H]+ + [OCI]-
        2. Principles of chlorination
          • ​​Water should be clear as turbidity impedes effective chlorination.
          • Chlorine demand of water:
            Amount of chlorine added- residual chlorine (after contact period of 60 minutes) Q.
          • Break point chlorination point at which chlorine demand of the water is met and if further chlorine is added free chlorine appears in water.
          • Minimum recommended concentration of free chlorine is 0.5mg/L.
          • Chlorine dose= chlorine demand of water+ free residual chlorine.
Method of chlorination
  1. Chlorine gas
  2. Chloramines (loose compound of chlorine & ammonia)
  3. Perchloron: HTH (high test hypochlorite); 60-70% of available chlorine.
  4. Super-chlorination
    1. Followed by de-chlorination.
    2. Addition of large amount of chlorine to water followed by removal of excess amount of chlorine.
    3. Suitable for heavily polluted water whose quality fluctuates.
  5. Ozonation & Ultraviolet irradiation: no residual effect.
Test to determine Chlorine cntent of water
  1. Orthotolidine test: estimates free and combined chlorine together.
  2. Orthotolidine- Arsenite test: estimates free and combined chlorine separately.
  1. Orthotolidine test
    Allows both free & combined chlorine in water to be determined with speed & accuracy; reagent consist of analytical grade o-tolidine dissolved in 10% solu of HCL which reacts immediately (10sec) with free chlorine producing yellow colour depending on the level of free chlorine but reacts slowly with combined chlorine(15-20min).
  2. Orthotolidine Arsenite Test:
    Determines levels of free & combine chlorine separately & errors due to presence of Fe, Mn & nitrites which produce yellow colour with OT are also overcome.

    (4B). Household purification of water​
    1. ​Boiling: roll boiling for 5-10 minutes.
    2. Bleaching powder: 33% of available chlorine.
    3. Stabilized bleach: bleaching powder+ excess lime
    4. Chlorine solution: 4 kg bleaching powder+ 20 litres water→5% chlorine solution.
    5. Chlorine tablets: 0.5 g for 20 litres of water.
    6. Filtration: Chamberland filter, Berkfeld filter & Katadyn filter.
    7. Disinfection of wells: double pot method.
Double pot method – to ensure constant dosage of chlorine to well water in emergency situations; can be left for 2-3wks containing 4500L of water with daily draw of 360 – 450L
  1. Bacteriological indicators for water quality
    1. Coliform organism: faecal group; E coli & non-faecal group; Klebsiella aerogens.
    2. Faecal streptococci: resistant to drying.
    3. Cl. perfringens: remote faecal contamination. (AI’09).

Extra Edge : Increase in nitrate level due to farming practices.

  1. Presumptive coliform test
    The test is done to assess whether the water has been contaminated or not. Presence of coliform organisms (E coli) suggests a fecal contamination of the water.
    1. Multiple tube method: 100 ml of water is taken and different quantities of this water are inoculated in tubes of MacConkey’s Lactose Bile Broth (0.1, 1.0, 10, 50 ml) and incubated for 48 hrs. From the number of tubes showing presence of acid and gas an estimate of most probable number of coliforms in 100 ml is obtained. This is done by consulting the Macardy’s chart.
    2. Confirmatory test: to confirm the presence of coliform organisms (only done for chlorinated water) the tubes positive in the earlier test are subculture in 2 tubes each of brilliant green bile broth; one of which is incubated at 37 degrees and the other at 44 degree Celsius. E coli is the only organism that can produce gas from lactose at 44 deg C.
  2. Hardness of water
    • ​​Bicarbonates of Ca & Mg: Temporary hardness
    • Sulphates of Ca & Mg: Permanent hardness
    • Fe, Mn, Al can all cause hardness
    1. ​​Classification
      • ​​Soft water - <1meq / L (<50 mg / L)
      • Moderately hard water – 1-3 meq / L (50 - 150mg / L)
      • Hard water – 3-6 meq / L (150 - 300 mg / L)
      • Very Hard water - >6 meq / L (>300 mg / L)
    2. Methods used for removing hardness of water are:
      • ​​Temporary hardness
        1. ​​Boiling
        2. Addition of lime
        3. Addition of NaHCO3
        4. Permutit process
      • Permanent hardness
        1. ​​Addition of Na2CO3
        2. Base exchange process

Test Your Skills Now!
Take a Quiz now
Reviewer Name