Quality of water

Pure water: It is a chemical compound (H₂O).

Potable Water: Water which is fit for drinking.

Palatable water: Water which is aesthetically looking good. Wholesome Water: Chemically may not be pure but doesn’t contain anything harmful to human beings.

Polluted Water: it contains undesirable substances rendering it unfit for drinking and domestic use.

Contaminated Water : It. contains pathogenic bacteria and unfit for drinking.

Mineral water: It contains useful minerals viz. Calcium. Magnesium and iron in required proportion.

CHARACTERISTICS OF WATER:

PHYSICAL CHARACTERISTICS

Turbidity :

• It is caused by suspended materials such as clay, silt or some other finally divided organic and inorganic matter. Turbidity is also due to presence of bacteria, algae, protozoa, fungi. Expressed in ppm (or mg/I)
• Standard unit is that which is produced by 1 mg. of finally divided silica (Fullers earth) in 1 liter of distilled water.
• Measured on ‘Silica Scale”
• Permissible limit for potable water 5 to 10 ppm
• Measured by: Turbidity meters

1. Jackson Turbid meter: Used to measure high turbidity (>25 p pm) -    (JTU)
2. Baylis Turbidity meter: precisely record even low turbidity values( of the order of 0 to 2 ppm.) BTU
3. Nephelometer : Commonly used for turbidity of range of 0 to 1 ppm-(NTU & FTU)—Fortmazin potymer is standard reference suspension. 

Turbidity Is the measure of resistance to the passage of light through water.

Colour:

• It is Caused by dissolved organic matters from decaying vegetation or some inorganic coloured soils, growth of algae, metallic ions (Fe and Mn).
• Measured by comparing the colour of water sample with other standard glass tubes (Nesslar tubes)
• Measured by Platinum Cobalt Method. (Measured on Platinum Cobalt Scale.)
• Permissible limit; 5 to 20 ppm.
• Measured by Tintometer..

Toste & Odour:

• Due to dissolved organic matter or inorganic salts, dissolved gases etc.
• Threshold number is the standard unit for measuring. .
• Taste is expressed as FTN (Flavor Threshold Number)
• Odour is expressed as TON (Threshold Odour Number)
• TN = Dilution ratio.
• Dilution Ratio= (A+B)/A                                                                                         
• A =Vol. of raw water sample
• B = Vol. of distilled water used for dilution.
• Permissible Limit: I to 3.
• The odour changes with tcmperature.
• it is tested normally at 20° C to 25° C.
• Odour is measured by an apparatus called osmoscope.

Osmoscope

The Osmoscope is graduated with Po values from 0 to 5.

Po value of O indicates ‘no perceptible odour’

Po value of 5 indicates ‘extremely strong odour’

Temperature: 100 C is desirable.

Specific conductivity: To know the dissolved salt content. Determined by Dionic water tester ,

Impurities in water:

Suspended impurities : They cause turbidity. The concentration of suspended impurities is measured by turbidity. eg : silt, clay, bacteria, fungi, algae.

Colloidal Impurities : These are finely divided dispersion of solid particles, not visible to the naked eye. These impurities if associated with organic matter having bacteria becomes the. chief source of epidemic.

Dissolved Impurities : h includes organic compounds. inorganic salts and gases. The following are various dissolved impurities and their effects.

1. Salts : CaCl2 , MgC1 , CO3 ,  HCO3, They cause hardness and alkalinity in water.
2. Metals : iron causes red colour, Manganese causes brown colour
3. Lead and arsenic cause poisoning
4. Gases : Oxygen causes corrosion of metals

• Chlorine and ammonia cause bad taste and odour
• CO2 and Hydrogen sulphide cause acidity in water.

CEMICAL CHARACTERISTICS 

Total solid , suspended solids and dissolved solid:

• Total solids can be found by evaporating a sample of water and weighing the dry residue left
• Suspended solids can be found by filtering water sample through Whatman filter paper No.44
• Permissible TDS limit: 500 to 1000 ppm

PH value of water: It indicates hydrogen ion concentration in water

• PH = log1o (l/H+),
• If pH >7 it is alkaline: If pH < 7 it is acidic
• Alkalinity is caused bicarbonates (HCO3) of Ca and Mg and carbonates (CO3), hydroxides (OH) of Ca. Mg, K. Na..
• Acidity is caused by Mineral Acids, Free CO2 Sulphates of Fe & Aluminum.

Alkalinity Effects : Incrustation and sediment deposit in pipelines and difficult in chlorination .

 Acidity Effects : Tuberculation & Corrosion of pipe lines.

• Permissible limit: 6.6 to 8.5
• PH is measured by Potentiometer and Colorimetric method.

Hardness:

A CHARACTERISTICS  which prevents formation of Lather or foam with soap.

Effects of Hardness : Scaling of boilers, greater: soap consumption, corrosion and incrustation of pipe lines, food becomes tasteless etc.,

Types of Hardness :

1. Carbonate hardness (CH) 
2.  Non Carbonate  hardness (NCH) .

Temporary or carbonate hardness : Caused by HCO3, and CO3 of Ca & Mg.

• Can be removed to some extent by simple boiling or removed fully by addition of lime.
• Permanent or non Carbonate hardness Caused by SO4, Cl, NO3 of Ca & Mg.
• Can be removed by water softening methods such as Lime soda process, Demilitarization process and Zeolite Process
• Permissible limits: For boiler feed waters < 75 ppm.
• For drinking purpose, between 75&115 ppm 
• If Hardness is <75 ppm is called ‘Soft’
• If Hardness is >200 ppm is called ‘Hard’
• Measurement: Measured in terms of ppm or mg/lit of CaCO3
•  Measured by EDTA test (Ethlyene Diamine Tetraacetic Test). In the titration process, Ericrome Black Tea is used to show the end of the titration .
• After determining amount of Ca & Mg ions presents in water, by nitration process with Versante solution, Hardness is estimated as followers

• 

Combining weight  or equivalent weight =Molecular weight/ Valence

• Hardness is also expressed in degree of hardness
• One British degree of hardness(Clark’s Scale) =14.25 ppm of CaCo3
• One French degree of hardness =10 ppm of CaCo3
• One American degree of hardness =17.15 ppm of CaCo3

Alkalinity in mg/l as CaCo3  =

Total Alkanity =HCo3 mg /L X (50/61) + Co3 mg/L X (50/30)

•  Chloride content: Present in the form sodium chloride imparts salty taste.
• Permissible limit :250 mg/l.Presence of the high quantity indicates pollution from sewage and other human & industrial waste.
• Nitrogen content Indicates presence  of   Organic matter and the extent to Which it has undergo decomposition.

 Different forms :

1. Free Ammonia 
2. Albuminoid Nitrogen  (organic nitrogen)
3. Nitrites             
4. Nitrates.

 Free  Ammonia indicates presence of under composed  organic  matter and it represents  first stage  decomposition

Permissible limit: less than 0.15 ppm

Albuninoid Nitrogen: Indicates decomposition of organic matter has started,limit shall not exceed 0.3 mg/lit

1. Nitrites: Indicates presence of partly decomposed organic matter.                                             Permissible limit : Nil
2. Nitrates:Indicates fully oxidized organic matter.                                                                               Permissible limit : <45 ppm

• Excess causes the disease called "Methemoglobenima " (Blue baby disease)
• Total Kjeldahl Nitrogen (TKN)=Free ammonia + organic nitrogen

Metal &Chemical Substance:

 Iron & Manganese: Permissible limit * Iron  <0.3 ppm, Mn <0.05 ppm.

• Excess Iron & Mn cause dis colouration of clothes washed in such water and incrustation of water mains due to deposits.

Copper : Permissible limit — 1 to 3 mg/l

• Affects human lungs and other respiratory organs

Sulphate: Permissible <250 mg /l

• Causes laxative effect en human body and diarrhea < 0.3 ppm.

 Fluoride:

• fluoride < 1 ppm, cause formation of fever cavities in the teeth.
• fluoride  > 1.5 ppm causes Flourosis (mottling and discolouration of teeth)and deformation of bones.
• Permissible limit: between 1 ppm and 1.5 ppm.

Dissolved  gases:

1. H2S                               
2. C02
3. Dissolved oxygen         
4. Nitrogen

• H2S gives bad taste and odour.
• CO2 indicates biological activity and causes corrosion in pipe lines.

Dissolved oxygen (D.O) : To know  the extent of pollution of water.

• Determined by Winkler's method
• Since D.O is consumed by unstable organic matter, D.O less than its saturated level indicates presence of organic matter, therefore pollution.
•  For fresh river water saturation D.O at 20°C = 9.2 mg/I.

Permissible Limit : For potable water should be bet 5 to 10 ppm.

Nitrogen gas: Indicates presence of Organic matter.

 Biochemical oxygen Demand (B. O.D)

Permissible Limits : B.O.D. of safe Water= Nil . 

 MICROSCOPIC CHARACTERISTIC

• To study about the presence of Bacteria,Virus, Algae. Protozoa.
• bacteria is single celled organisms

1 Bacteria (I to 4 microns in size) :

Classification

1. Non pathogenic bacteria: They are harmless; e.g Escherichia coliform or E-coil
2. Pathogenic bacteria: They are harmful & causes water borne disease.

• Detection of “E-Coil”Indicates the probable presence of 'pathogens’
• E — Coil bacteria is used as indicator organism

Classifaction based on shape:.

• Cocci — Sphere shaped bacteria
• Bacilli — Rod shaped bacteria
• Spirilla — twisted rod shaped bacteria

Classification based on living conditions;

1. Aerobic bacteria: It survives in the presence of Oxygen.

2. Anaerobic bacteria: It survives in the absence of Oxygen.

3. Facultative bacteria: Survives with or without Oxygen.

To detect and measure coliform bacteria, the following tests are available.

• 1 .Total count or agar plate count fest
• 2. E—coil test :
• 3. Membrane filter technique

Total count test : In this test bacteria are cultivated on specially prepared medium of agar for different dilutions of sample of water with distilled water. The diluted sample is placed in an incubator for specified time at specified temperature. The bacteria colonies so formed are counted and results are computed  per 100 ml

• For drinking water, the total count shall not be more than 1 per 100 ml

E — coil test : Divided into

1) Presumptive test

2) Confirmed lest

3) Completed test

In this test gas produce after incubation, it is reported as positive and further tests are to be followed to confirm E-coil. If no gas is produced it is presumed that there is no bacteria and the test is treated as negative

Membrane filter technique: Recent method. Sample is filtered through sterile membrane

with pore size 5 to 10 mu. The bacteria is retained on the membrane. The membrane is put in contact with suitable nutrient. [ M — Endo’s medium ] which inhibits growth of bacteria other than coil form group. Then 

placed in incubator at prescribed conditions and the visible colonies are counted with microscope.

MPN (Most Probable Number): It is the bacterial density which is most likely to be present in water. It is used to report the amount of bacteria present. 

• To determine MPN, confirmed or completed tests results are required.
• Permissible limits : - MPN should be Nil.

Micro Organic Plants: Thesc are tiny plants. eg: Algae, plankton etc 

• They cause bad taste & odour and interface with smooth working of filter.
• To control algae, copper sulphate chemical is mixed in water

 Protozoa: These are unicellular animals.

Water borne diseases: Diseases which spread primarily through contaminated, water and

important of these water borne diseases are:

Bacterial infections:

• Typhoid fever 
• Diarrhea
• Cholera 
• Bacillary dysentery

Viral infections:

• Infection Hepatitis 
• Poliomyelitis.
• Gastroenteritis

Protozoal infections:

• Amoebic dysentery.