PHYSICAL CHARACTERISTICS OF WATER
Following are the physical characteristics of water :
1) Temperature :
For drinking purpose temperatures around 10°C are highly desirable, while temperatures above 25°C are considered objectionable.
2) Colour :
Pure water is colourless, but water gets coloured because of presence of foreign substance.
Colour of water is because of substances within the true solution or in colloidal suspension.
Colour imparted by suspended matter is claimed to be apparent colour which by dissolved solids is named true colour.
Decaying organic matter like leaves, peat, logs, weeds etc impart colour to the water. Presence of iron, manganese, algae and industrial waste (dye, textile etc) also impart colour to the water.
Coloured water isn’t aesthetically and psychologically acceptable i.e people might not wish to drink coloured water even it’s going to be safe from other point of view. It also spoils the color of the garments .
Coloured water is additionally not suitable for a few industries like paper, dyeing, textile etc.
Coloured water can acts as a clear sign of water being polluted by the industries or decaying organic matter it’s measured by comparing water with the quality solution of platinum cobalt or standard colour glass disc.
The quality unit of colour is that which is produced by one milligram of platinum cobalt dissolved in one litre of water .
The intensity of colour is measure in terms of arbitrary unit of colour on cobalt scale.
An instrument called tintometer is used to measure the color .
For drinking purpose the color number on cobalt scale shouldn’t exceed 20 and will be preferably but 10.
3) Taste and odour :
Pure water should be odourless and will have a reasonably quality (actually pure water is tasteless).
Taste and odour is because of presence of dissolve gases like H₂S , CH₄ , CO₂ , O₂ ,etc, dissolved organic matter, algae, mineral salts like NaCl, iron compounds, chemicals like phenols, tarry substance, industrial waste etc.
Taste imparted by dissolved oxygen and CO₂ is desirable. For drinking purpose water must not have objectionable taste and odour.
Consumers find taste and odour aesthetically displeasing as they associate it with some sort of contamination.
Odour is measured in terms of threshold number. The minimum odour which will be detected is named Threshold Odour Number (TON).
The value of TON is decided as follows :
TON = (A + B)/A
A Volume of sample in ml
B = Volume of distilled water
For public water supplies TON shouldn’t be greater than 3.
An instrument called Osmoscope having two tubes is use for odour test.
4) Turbidity :
Turbidity is that the cloudiness or haziness in water caused by colloidal material like clay, silt, rock fragments, and microorganisms.
Turbidity may be a measure of the extent to which light is either absorbed or scattered by the suspended matter in water.
The turbidity depends upon the fineness and concentration of particles present in water.
Although, the clay or other inert suspended particles might not be harmful to health, yet it’s aesthetically displeasing.
Colloidal particles also can acts as shield for microorganism, so disinfection of turbid water can’t be done properly.
Turbidity is measured by :
1. Turbidity rod
2. Jackson turbidimeter
3. Baylis turbidimeter
Turbidity is expressed by the quantity of suspended matter in parts per million (ppm) by weight in water.
For water 1 ppm is like 1 mg/litre. the quality unit of turbidity is that produced by 1 a part of finely divided silica in million parts of water .
JTU(Jackson Turbidity Unit, obtained by Jackson turbidimeter) and NTU (Nephlometric Turbidity Unit obtained by nephlometer) also are the units during which turbidity is measured.
Jackson turbidimeter can’t be used for measuring turbidity but 25 JTU. (1 JTU = 1ppm).
For measuring lesser turbidity Baylis turbidimeter is employed . It can measure turbidity less than 5 ppm also accurately.
Nephometer features a very wide selection (0 to 2000 ppm) The permissible limit of turbidity for public water supplies is 5 to 10 ppm.
5) Conductivity :
It gives a thought about the dissolved solids in water.
Greater the quantity of dissolved solids higher are going to be the conductivity.
It is often measured easily with the assistance of conductivity meter.
The typical value of conductivity for potable water should be but 2 mho/cm.