1. Hardness of Water
   1. Soap destroying power of water
   2. Types of hardness
      1. Temporary hardness (Carbonate hardness)
         1. Cause
            1. Calcium & Magnesium salts of Bicarbonates
         2. Methods of removal
            1. -Boiling -Addition of lime -Addition of sodium carbonate -Permutit process
      2. Permanent hardness (Non- Carbonate hardness)
         1. Cause
            1. Ca & Mg salts of Sulfates, Chlorides, Nitrates
         2. Methods of removal
            1. -Addition of sodium carbonate -Base exchange process/Permutit process
   3. Classification of hardness in water
      1. Soft water
         1. < 1
      2. Moderately Hard water
         1. 1 – 3
      3. Hard water
         1. 3 – 6
      4. Very Hard water
         1. > 6
2. PURIFICATION OF WATER ON A LARGE SCALE
   1. Storage of water:
      1. Physical :90% suspended impurities settle down
      2. Chemical : Organic matter oxidized by aerobic bacteria
      3. Biological : pathogenic organisms die during storage
   2. Filtration of water:
      1. - Slow sand (Biological) filters
         1. Schmutzdecke / Vital layer Slimy growth covering the sand bed in slow sand filter -Heart of slow sand filter -Its formation is called ripening of the filter
      2. - Rapid sand (Mechanical) filters
         1. Back washing
            1. -Reversing the flow of water through the sand bed
   3. Comparison of Rapid and Slow Sand Filters
      1. Space
         1. Occupies very little space
         2. Occupies large area
      2. Rate of filtration
         1. 5-15 cubic meter /hour/ sq. m of sand bed
         2. 0.1-0.4 cubic meter /hour/ sq. m of sand bed
      3. Effective size of sand
         1. 0.4 – 0.7 mm
         2. 0.2 – 0.3 mm
      4. Preliminary treatment
         1. Coagulation, sedimentation
         2. Plain sedimentation
      5. Washing
         1. By back-washing
         2. By scraping sand bed
      6. Frequent washing
         1. Required
         2. Not required
      7. Mechanism of action
         1. Essentially physical
         2. Both physical & mechanical
      8. Loss of head allowed -Reduced efficiency of filters due its clogging
         1. 6 – 8 feet
         2. 4 feet
      9. Removal of bacteria
         1. 98 – 99 percent
         2. 99.9 – 99.99 percent
      10. Suitability
          1. For big cities
          2. For small towns
   4. Disinfection of water:
      1. - Chlorination - Ozonation - Ultraviolet irradiation
3. PURIFICATION OF WATER ON A SMALL SCALE
   1. Household purification of water
      1. 1. Boiling
      2. 2.Chemical disinfection:
         1. -Bleaching powder -Chlorine solution -High test hypochlorite (HTH) -Chlorine (Halozone) tablets -Iodine -Potassium permanganate
      3. 3. Filtration:
         1. Ceramic filters : Pasteur Chamberland filter Berkefeld filter Katadyn filter
4. CHLORINATION OF WATER
   1. Disinfecting action of chlorine in water is due to: Hypochlorous acid
      1. Has residual germicidal effect
   2. Break point chlorination
      1. Addition of chlorine to water to a point at which free residual chlorine begin to appear
   3. Chlorine demand
      1. Difference b/w amt of chlorine added to water & amt. of residual chlorine remaining at the end of a specific period of contact at given temp and pH of water
      2. Horrock's apparatus used to measure chlorine demand
   4. Free residual chlorine
      1. Recommended contact period in water: > 0.5 mg per litre (ppm) for 1 hour
   5. Methods of chlorination
      1. Chlorine is applied either as Perchloron Chlorine gas Chloramine Breakpoint chlorination Superchlorination
5. OTHER KEY POINTS
   1. Potable water
      1. -Free from pathogens, harmful chemicals, color, odor. -Pleasant to taste -Useful for all domestic needs
   2. Water supply
      1. Drinking 2L per head per day
      2. Domestic needs 150-200L per capita
   3. Problem village Acc. to National water supply & sanitation programme
      1. -No source of safe water within a distance of 1.6 km -Water available at a depth of > 15m -Water exposed to risk of cholera -Water has excess salinity/iron/fluorides/toxic elements
6. Disinfection of wells:
   1. Double pot method by NEERI,Nagpur
   2. Chemical used: Bleaching powder