WATER

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  • WATER
    • Purest water in nature is Rain water
    • SOURCES OF WATER:
      • Rain:
        • Is the prime source of all water
        • Is the ‘purest form of water in nature’
        • Chemically, it is very soft water: contains traces (0.0005%) of solids
        • Gibraltar depends on rain water as a source of supply
      • Surface water:
        • Impounding reservoirs
        • Artificial lakes for storing large quantities
        • Mumbai, Chennai, Nagpur derive water from it
        • Next to rain water in purity
      • Rivers and streams
        • Grossly polluted; unfit for drinking without treatment :
        • Delhi, Kolkata, Allahabad derive water from it
      • Tanks, ponds and lakes
      • Ground water:
        • Shallow wells
          • Moderately hard, grossly contaminated water
          • Taps water from above 1st impervious layer
        • Deep wells
          • Much hard, pure water; constant supply
          • Taps water from below 1st impervious layer
        • Springs
  • Safe and wholesome water : has been defined as water that is
    • Free from pathogenic agents
    • Free from harmful chemical substances
    • Pleasant to taste (free from colour and odour)
    • Usable for domestic purposes
  • Water is said to be ‘polluted’ or ‘contaminated’ if it does not fulfill above criteria
  • Safe yield of water: Yield that is adequate for 95% of the year
  • Break point chlorination,
    • Free chlorine is released in water after break point chlorination (MCQ)
    • Chlorine demand is the amount needed to kill bacteria, oxidize organic matter and neutralize ammonia
    • Contact period of 1 hour is necessary (MCQ)

CHLORINATION OF WATER: (High yield Topic for PG Medical entrance)

  • Disinfecting action of chlorine in water is due to:
    • Hypochlorous acid (HOC1) – Main role in disinfection
    • Hypochlorite ions (OC1) – Minor role in disinfection
  • Chlorine has residual germicidal effect (and not Ozone or UV rays): Provides a margin of safety against subsequent microbial contamination, as may occur during storage and distribution
    • Phases of Chlorination:
    • Phase I: Formation of chloramines
    • Phase II: Destruction of chloramines
    • Phase III: Appearance of break-point
    • Phase IV: Accumulation of free residual chlorine
  • Recommended contact period of free residual chlorine in water: I hour
  • Level of free residual chlorine (FRC) recommended:

(* 1 mg per litre = 1 ppm)

  • Correct dose of chlorine to be applied: Chlorine demand + FRC 0.5 mg per litre : (MCQ)
  • Bleaching power (CaOCl2) contains : 33% available chlorine : (MCQ)
  • Chlorine acts best as a disinfectant for water at : pH around 7.0 : (MCQ)
  • Instruments used in chlorination of water : (MCQ)
  • Order of instruments to be used in chlorination of water. Horrock’s Apparatus, Chlorinator/ Chloronome, Chloroscope
  • Tests for chlorination of water.
    • Ortho-toulidine (OT) Test: Measure the levels of,
      • Free chlorine
      • Free & Combined chlorine
    • Ortho-toulidine Arsenite (OTA) Test: Measure the levels of,
      • Free chlorine
      • Combined chlorine
    • OTA test is better than OT test as:
      • detects both free and combined chlorine separately
      • not affected by interfering substances (nitrites, iron, manganese)
    • Ortho-toididine (OT) test:
      • Reagent used: O-toulidine in 10% solution of hydrochloric acid
      • Dose added; 0.1 ml reagent to 1 ml of water
      • Colour change in presence of chlorine: becomes yellow
      • Readings:
        • Within 10 seconds: Free chlorine
        • After 10 — 20 minutes: Free and Combined chlorine
  • Nitrates in excess of 45mg/l  may cause infantile methaemoglobinaemia – ‘Blue baby syndrome’
  • Guideline value of nitrate in drinking water: < 50 mg/litre
  • Nitrates in drinking water indicate: Remote contamination
  • Guideline value of nitrite in drinking water: < 3 mg/litre
  • Nitrites in drinking water indicate: Recent contamination
  • (Concentration of nitrate/Guideline value of nitrate) + (Concentration of nitrite/Guideline value of nitrite ) should be < 1
  • Bacteriological indicators of water quality: (MCQ)
    • Coliforms (E.coli is most important microbiological indicator)
    • Fecal streptocococci (Indicator of recent contamination) (MCQ)
    • Clostridium perfringens (Indicator of remote contamination) ) (MCQ)
    • Acceptable level of coliforms in drinking water: None
    • EXCEPTION: In large urban supplies, upto 5% samples are acceptable to be contaminated, if taken continuously for a period of 12 month
  • Coliform organisms:
    • Primary & most reliable bacterial indicator for water quality
    • coli is most important coliform indicator
    • Reasons for choosing coliforms as indicators of fecal pollution RATHER THAN WATER – BORNE
  • Per capita allowance of water per day is recommended at 150-200 lit
  • Water supply considered adequate to meet the need for domestic purposes:
    • Urban: 150-200 litres per capita per day
    • Rural: 40-60 litres per capita per day
    • Daily drinking water requirement: 2-3 litres per capita per day
  • Criteria for identification of ‘Problem Habitations’:
    • Not Covered (NC/No Safe Source {NSS) Habitations:
      • Drinking water source point is not within 1.6 kms in plains or 100 m elevation in hilly areas
      • Water source affected with quality problems like excess salinity, iron, fluoride, arsenic, or other toxic materials or biologically contaminated
      • Quantum of availability of safe water is not enough to meet drinking and cooking needs
    • Partially Covered (PC Habitations)
      • Drinking water source point is within 1.6 kms in plains or 100 m elevation in hilly areas
      • Capacity of system is 10-40 liters per capita per day potable wate
    • Fully Covered (FC) Habitations’, include all the remaining habitations
  • Hardness of Water   (Very High yield topic in PG Medical Entrance exam)
    • Temporary hardness of water is primarily due to the presence of Calcium & magnesium bicarbonates (MCQ)
    • Hardness of water is defined as the ‘soap destroying power of water’
    • Hardness of water is of two types: Hardness of water is expressed in terms of: milliequivalents per litre (meq/lt) of CALCIUM CARBONATE (CaCO3)
  • 1 meq/lt hardness = 50 mg CaCO3 (50 ppm) per litre of water
  • Classification of hardness in water:
  • Horrock’s apparatus estimates Chlorine demand (MCQ)
  • Use: To find out the dose of bleaching powder required for disinfection of water, i.e. ‘Chlorine demand estimation of water’
  • Contents:
    • 6 white cups (200ml capacity each)
    • 1 Black cup (with a circular mark inside)
    • 2 metal spoons
    • 7 glass stirring rods
  • Indicator: Starch iodide (producing blue colour)
  • Dose of bleaching powder required (Chlorine demand):
  • n X 2 gms to disinfect 455 litres of water (where n = of first cup which shows distinct blue colour)
  • Development of blue colour indicates: presence of free residual chlorine
  • Chlorine demand of water. : 3 common facts as MCQs
  • Is the amount of chlorine that, is needed to destroy bacteria, and to oxidize all the organic matter amd ammonical substances present in water
  • Is the amount of chlorine added to water minus amount of residual chlorine remaining at the end of a specific period of contact (1 hr)
  • Estimation of chlorine demand of water (or dose of bleaching powder required for disinfection of water) is done by ‘Hoirock ‘s apparatus’

PURIFICATION OF WATER:

  • Purification of water on a large scale:
    • Storage of water
      • Physical
      • Chemical
      • Biological
    • Filtration of water
      • Slow sand (Biological) filters
      • Rapid sand (Mechanical) filters
    • Disinfection of water
      • Chlorination
      • Ozonation
      • Ultraviolet irradiation
    • Purification of water on a small scale:
      • Household purification of water:
        • Boiling
        • Chemical disinfection: Bleaching powder, Chlorine solution, High test hypochlorite (HTH),
          • Chlorine (Halozone) tablets, Iodine, Potassium permanganate
        • Filtration: Ceramic filters (Pasteur Chamberland filter, Berkefeld filter, Katadyn filter)
      • Disinfection of wells:
        • Chemical: Bleaching powder (Double pot method)
      • Desirable and Undesirable water
        • Most desired temperature range for drinking water is 40- 50° F
        • Most undesirable metal in drinking water is Lead
        • Undesirable metals in drinking water: Iron, manganese, zinc, copper, aluminium, lead
        • Lead was earlier seen in drinking water when water was being supplied through lead pipes
        • Undesirable salts in drinking water: Chlorides, Fluorides, Nitrites, Nitrates, Calcium, Magnesium

Undesirable gases in drinking water: Ammonia, Hydrogen sulphide, Methane

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