Water, Water cycle, water impurities and water purifier


After air, water is the most essential commodity for the continuation of life.It has been estimated that two third of human body is constituted of water.

Water cycle

Evaporation of water take place due to sun heat converting into clouds which under favorably condition causes precipitation and those the rain water flow into lakes, river.Then to see such a cycle of evaporation and precipitation is known as water cycle.

Sources of water

Various sources of water available on the earth can be classified into the following two categories:-

  1. Surface sources:

  • Ponds and lakes
  • Streams and rivers
  • Storage reservoirs,impounding reservoir
  • Ocean, generally not used for water supply at present.

      2. Sub-surface sources or underground sources:

  • Spring 
  • Infiltration galleries 
  • Infiltration Wells 
  • Wells and tube-wells

Quality of water 

An absolutely pure water is not recommended for women health as this water does not contain certain minerals which are very essential to health. Thus the wholesome water is neither chemically pure not  it contain anything harmful to human health.

Quality of water for public water

  • It should be cool and colourless.
  • It should be odourless and tasteless.
  • It should be free from disease carrying bacteria.
  • It should be fresh.
  • It should be free from excessive amount of organic matter and mineral.
  • It should not corrode the pipe.
  • It should be free from poisonous materials.

Examination of water 

The raw or treated water can be checked and analysed by studying and testing their physical and chemical properties.

Physical characteristics

Taste or Order
Specific conductivity

  1. Turbidity (muddiness of water)

It is measured by turbidity rod or by  turbiditimeter with optical observations and is expressed as the amount of suspended matter in mg/l or part per million(p.p.m)

  • For water, ppm and mg/l are approximately equal.
  • For drinking water turbidity of less than 10 p.p.m is desirable. The optimim is 5 p.p.m

      2. Colour

The presence of colour in water is not objectionable from health point of view,but may spoil the colour of clothes being washed.

  • The colour for potable water is 10 to 20 p.p.m on Platinum Cobalt scale
  • Colour determined by an instrument is known as tintometer.

      3. Taste and order

Taste in water main result from any one or combination of micro-organism either dead or alive dissolved gases such as dihydro sulphate, methane, carbon dioxide or oxygen combine with organic matter.

  • For public supplies, the water should generally free from odour e.g. the threshold number should be 1 and should never exceed 3.

      4. Temperature

The most desirable range of temperature for a public water supply is seldom below 40 to 50’F.

  • For potable water temperature of about 10 degree Celsius are highly desirable.It should not more than 25 degree Celsius.

      5. Specific conductivity

The total amount of dissolved salt present in water can be easily estimated by measuring the specific conductivity of water

Chemical characteristics

  1. Total solid and suspended solids
  2. pH value of water
  3. Hardness of water
  4. Chloride content 
  5. Nitrogen content
  6. Metal and other chemical substance 
  7. Dissolved gases

  1. Total solid and suspended solids

  • Total permissible amount of solid in water is generally limited to 500 p.p.m
  • The suspended solid can be found by filtering the water sample.

       2. pH value of water

  • The pH value of water can be measured quickly and automatically with the help of a potentiometer.
  • Permissible pH value for public supplies may range between 6.6 to 8.4
  • The lower value of pH cause tuberculation and corrosion.
  • The higher value of pH may cause incrustation,sediment deposits, difficulty in chlorination.

      3. Hardness of water

Hard water are undesirable because they may lead to greater soap consumption, scaling of boiler
Causing,corrosion and incrustation of pipes, making food tasteless.Bicarbonate and carbonate of calcium and magnesium are present in water the water is rendered hard temporary as this hardness can be removed to some extent by simple boiling or to fill extent by adding lime to water such a hardness is known as temporary hardness and carbonate hardness

  • Water with hardness up to 75 p.p.m are considered soft and above 200 p.p.m are considered hard.In between moderately hard.
  • The prescribed hardness limit for public supplies range between 75 to 115 p.p.m.
  • Underground water is generally hard water.

       4. Chloride content 

  • The chloride content of treated water to be supplied to the public should not exceed a value of about 250 p.p.m.

        5. Nitrogen content :

  • Free ammonia :- It indicates very first stage of decomposition of organic matter it should not exceed 0.15 mg/l.
  • Nitrites:- Not fully oxidized organic matter in water.It is highly dangerous and its limit in potable water is nil.
  • Nitrates :- It indicate fully oxidized organic matter in water nitrate in water is not harmful However the presence of too much of nitrates in water may adversely affect the health of infants causing a disease technically called mathemoglobinemia commonly called blue baby disease.

        6. Biological oxygen demand (BOD)

  • The BOD of safe drinking water must be nil.

Purification of water supplies (method of purification of water)

  1. Screening :- To remove floating matter e.g.  bushes, dead animals, leaves branches of trees etc.
  2. Plain sedimentation:–  To remove suspended impurities e.g.  sand, silt and  clay etc.
  3. Sedimentation with coagulation :- To remove fine suspended matter
  4. Filtration:- To remove micro organism.
  5. Disinfection :- To remove bacteria.
  6. Aeration and chemical treatment :- To remove dissolved gases taste and odour.
  7. Miscellaneous treatment such as fluoritation, recarbonation, liming, desalination etc

Water demand (various type of water demand (litre per capita per day (lpcd))

  • Domestic water demand 55 to 60 percent of total water consumption.
  • Industry water demand 50 lpcd
  • Industrial and commercial water demand 20 lpcd
  • Demand for public School 10 lpcd
  • Fire demand 1 lpcd.
  • Water required to compensate loose in waste and theft 55 lpcd

Factor affecting per capita demand

  • Size of the city
  • Climate condition
  • Type of gentry and habit of people
  • Industrial and commercial activities
  • Quality of water
  • Pressure in the distribution system
  • Development of sewage facilities
  • System of supply
  • Cost of water
  • Policy of metering and method of charging

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