Physical water quality parameters

QUALITY PARAMETERS OF WATER

Water impurities are classified as physical, 

chemical and biological impurities 

 PHYSICAL WATER QUALITY PARAMETER 

 Suspended solids,

 Turbidity,

 Colour,

 Taste and odour,

 Temperature

SUSPENDED SOLIDS 

Source: 

These are called as physical parameters 

whereas dissolved solids are considered as 

chemical parameters. Suspended solids 

comes from inorganic particles like silt, clay 

etc., Immiscible liquids like oils and greases 

and organic particles like plant fiber, algae, 

etc. Inorganic solids are non-degradable 

solids. 

Note: Problem of Suspended Solid comes only in surface water not in ground water. 

Objection: 

These are objectionable because 

(a) Aesthetically displeasing. 

(b)It provides adsorption sites for 

chemical and biological agents

(c) They may also be biologically active and 

may form disease causing organisms as 

well as organisms such as toxin 

producing strains of algae. 

Measurement 

 Most of the methods are gravimetric i.e.

SS are calculated by weighing them.

 Total solids i.e. all solids (suspended or

dissolved) are calculated by

evaporating the sample and measuring

the residue. Heating temperature is 

104°C. Suspended solid is obtained by

filtration and heading the residue on

filter at 104°C Dissolved solids (DS) = Total solids (TS)– Suspended solids(SS)

Note: Filtration in real terms does not 

exactly divides the solids into 

suspended and dissolved fractions 

because some colloids may pass 

through the filter and can get measured 

along with dissolved fraction. Hence, 

classification is does as filterable solids. 

Hence suspended solids are 

corresponding to non – filterable solids 

and dissolved solids are corresponding 

to filterable solids. 

 The organic content of both total and

dissolved solid can be determined by

firing the residue at 6000C.

Organic fraction

600CCO2 + Water + 

Other gases

The Permissible limits 

For suspended solid as per EPA 

(Environmental Protection Agency) is 30 

mg/l 

TURBIDITY 

Source: 

Turbidity is the measure of extent to which 

light is either absorbed or scattered by 

suspended material in water. It is not a 

direct quantitative measure of suspended 

solids. 

Objection:

 Disinfection of turbid water is difficult

because the suspended solids may

partially shield the organisms from

disinfectant.

In natural bodies, turbidity interferes 

with light penetration and hence with 

the photosynthetic reactions (which 

gives oxygen to the water).

Measurement

Measurement of turbidity is done using the 

following:

 Turbidity rod

 Jackson’s turbid meter

 Baylis turbid meter

 Nephlometer 

Turbidity rod

 Rod with platinum needle is inserted 

water and the depth at which platinum 

needle just becomes invisible gives 

turbidity in ppm.

 As depth of insertion increases, reading 

will decrease.

 Turbidity which one milligram of finely 

divided silica produces in one liter of 

distilled water is taken as one unit.

 The permissible limit is 5 – 10 ppm.

 It is a field method. 

Note:GOI manual gives turbidity in NTU 

i.e. Nephelometer turbidity unit. Acc

Jackson’s Turbid meter

 The level of water is increased till the 

image of flame ceases to be seen.

 The turbidity is measured from 

graduated glass tube.

 It is used when turbidity is greater than 

25 ppm.

 It is a laboratory method.

 This method is not used for drinking 

water.

Note:Turbid raw water of natural 

source has turbidity greater than 25 

ppm.

Baylis Turbid meter and Nephelometer

 Baylis and Nephelometer turbid meters 

are based on colour matching techniques.

 In this case even a small turbidity of one 

unit or less can be measured.

 Hence these are most widely used for 

domestic water supplies.

 In Baylis turbiditymeter light intensity 

is measured in the direction of incident 

light only where as in Nephelometer 

light intensity is measured as right 

angles to the incident ray.

 Hence NTU is based in Scattering 

principle.

 If Formazine, a chemical, is used as base 

in place of SiO2. The turbidity is also 

sometimes called FTU.

 COLOUR

Source

Colour is caused by suspended and 

dissolved matter in water.

 After suspended matter causing colour 

is removed by centrifugation, the colour 

obtained is called true colour.

 Humic acid gives yellowish brown 

colour, Iron oxide gives reddish colour, 

manganese oxide gives brown or 

blackish water.

 Water containing oxidized iron and 

manganese impart characteristic 

reddish or black colour. Heavy growth 

of algae may also impart colour to the 

water.

Objection

 Coloured water is not suitable for dying 

purpose.

 Organic compounds causing colour may 

exert chlorine demand and hence 

reduces the effectiveness of disinfection 

by chlorine.

 Phenolic compound with chlorine 

produces taste and odour.

 Some colour causing organic 

compounds with chlorine becomes 

carcinogenic.

Measurement

 Measurement of colour is done by colour 

matching technique (tintometer).

Result is expressed in TCU or Hazen 

unit (True colour unit) where 1 TCU is 

equal to color produced by 1 mg per 

litre of platinum in the form of 

chloroplatination (It is only for 

yellowish brown color)

 For colour other than yellowish brown 

i.e. from industrial effluent, spectro 

photometric technique is used.

 The colour testing is done within 72 

hours of collection as otherwise 

biological or physical properties may 

change.

Permissble limit: Acceptable limit is 5 

TCU and cause for rejection is 25 TCU.

 TASTE AND ODOUR

 Taste and odour are caused by dissolve 

gasses like H2S (Hydrogen sulphide), 

mercaptans, methan, organic matter 

derived from certain dead or living 

microorganism, decomposing organic 

matter, industrial liquid, waters 

containing phenols , cresols , ammonia , 

agricultural chemicals, high residual 

chlorine and chloro-phenols.

Source

 Sulphur imparts rotten egg like taste 

and odour.

 Algae secretes oily substances that may 

result in bad taste and odour.

Objection: The taste and odour causing 

compounds may be carcinogenic.

Measurement

 Measurement of taste and odour 

causing organics can be done using gas 

or liquid chromatography. However this 

method is costly and not done in 

routine.

 Odour is generally measured by an 

instrument known as somoscope.

 Intensity of taste and odour is 

measured by Threshold odour 

number. (TON)

 It represents the dilution ratio at which 

odour is hardly detectable.

 TON allowed is between 1 – 3.

 TON testing is done in cold water 

because increase in temperature may 

Change the taste and odour.

 The formula for TON = 

A+B/A

where A is 

the volume of odours water in mL and B 

is the volume of odour free water 

required to procedure a mixture in 

which odour is hardly detectable.

 Odour can be removed by mechanical 

aeration, oxidation by chemicals like 

chlorine or its compounds or ozone or 

permanganate and adsorption of odour 

by agents such as activated carbon. Floc 

or clays.

Temperature

 Temperature affects the chemical and 

biological reactions. An increase in 10°C 

, doubles the biological activity. Hence 

for water supply, the temperature 

should be between 10-25°C and greater 

than 25°C is objectional.