Physical Characteristics of Water

 

 

 Physical feature of water

 

Physical feature of water are:

1: Color                                   2: Turbidity    

3: Taste and odor                 4:  Temperature   

5:  Solids

Physical characteristics of water (temperature, color, taste, odor and turbidity etc.) are determined by senses of touch, sight, smell and taste. For example temperature by touch, color, floating debris, turbidity and suspended solids by sight, and taste and odor by smell.

1:  Color :

Color in water is primarily a concern of water quality for aesthetic reason. Coloured water gives the appearance of being unfit to drink, even though the water may be perfectly safe for public use. On the other hand, color can indicate the presence of organic substances, such as algae or humid compounds. More recently, color has been used as a quantitative assessment of the presence of potentially hazardous or toxic organic materials in water.

A: Color – pure water is colorless

B: Colored water can indicate pollution.

C: Color can also show organic substances.

D: The maximum acceptable level for the color of drinking water is 15 TCU (True color unit).

 Further Explanation:

The presence of colour in water is not objectionable from health point of view, but may spoil the colour of the clothes being washed. The standard unit of colour is that which is produced by one milligram of platinum cobalt dissolved in one litre of distilled water.

For public supplies, the colour number on cobalt scale should not exceed 20 and should be preferably less than 10.

 

Measurement:

Colour determined by an instrument is known as “Tintometer”.

2:  Turbidity :

Turbidity is a measure of the light-transmitting properties of water and is comprised of suspended and colloidal material. It is important for health and aesthetic reasons.

Turbidity – pure water is clear and does not absorb light. If turbidity appears in the water, it may indicate water pollution.

1. Turbidity of Water

The turbidity is measured by a turbidity rod or by a turbidity meter with optical observations and is expressed as the amount of suspended matter in mg/l or parts per million (ppm).

Ø  For water, ppm and mg/l are approximately equal.

Measurement:

1: Turbidity Rod:

The turbidity can be easily measured in the field with the help of a turbidity rod. It consists of an aluminium rod which is graduated as to give turbidity directly in silica units (mg/l)

 

2: Turbidimeter:

The turbidity can be easily measured in the laboratory with the help of a instruments called turbidity meter. In general, a turbidity meter works on the principle of measuring the interference caused by the water sample to the passage of light rays.

 

The height of water column will therefore be more for less turbid water and vice versa. Longer the light path lower the turbidity. Such a turbidimeter cannot measure turbidities lower than 25 JTU.

It can be used for natural sources only and cannot be used to measure the turbidity of treated water supplies,

One of the two glass tubes is filled with water sample (whose turbidity I to be measured) and the other is filled with standard water solution of known turbidity. The electric bulb is lighted and the blue colour in both the tubes is observed from the top of the instrument.

 

3:  Taste and Odor :

Taste and odor are human perceptions of water quality. Human perception of taste includes   sour (hydrochloric acid),

salty (sodium chloride),

sweet (sucrose) and

 bitter (caffeine).

Explanation:

Relatively simple compounds produce sour and salty tastes. However sweet and bitter tastes are produced by more complex organic compounds. Human detect many more tips of odor than tastes. Organic materials discharged directly to water, such as falling leaves, runoff, etc., are sources of tastes and odor-producing compounds released during biodegradation.

 > Taste and odor – pure water is always tasteless and odorless. If any type of taste and smell is present, it may indicate water pollution.

The extent of taste or odor present in a particular sample of water is measured by a term called odor intensity, which is related with the threshold odor or threshold odor number.

Measurement:

Water to be tested is therefore gradually diluted with odor free water, and the mixture at which the detection of odor by human observation is just lost, is determined. The number of times the sample is diluted represents the threshold odor number.

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

 

 

 

4: Temperature :

The temperature of water affects some of the important physical properties and characteristics of water:

1: Thermal capacity,

2: Density,

3: Specific weight,

4: Viscosity,

5: Surface tension,

6: Specific conductivity,

7: Salinity and Solubility of dissolved gases and etc.

 Chemical and biological reaction rates increase with increasing temperature. Reaction rates usually assumed to double for an increase in temperature of 10 °C. The temperature of water in streams and rivers throughout the world varies from 0 to 35 °C.

Temperature – the temperature is not directly used to evaluate whether water is drinkable or not. However, in natural water systems like lakes and rivers, the temperature is a significant physical factor that determines water quality.

 

5:  Solids :

The total solids content of water is defined as the residue remaining after evaporation of the water and drying the residue to a constant weight at 103 °C to 105 °C. The organic fraction (or volatile solids content) is considered to be related to the loss of weight of the residue remaining after evaporation of the water and after ignition of the residue at a temperature of 500 °C. The volatile solids will oxidize at this temperature and will be driven off as gas. The inorganic (or fixed solids) remind as inert ash. Solids are classified as settle able solids, suspended solids and filterable solids. Settle able solids (silt and heavy organic solids) are the one that settle under the influence of gravity. Suspended solids and filterable solids are classified based on particle size and the retention of suspended solids on standard glass-fiber filters.

Solids – If water is filtered to remove suspended solids, the remaining solid in the water indicates the total dissolved solids. If the dissolved solids in the water exceed 300 mg/l, it adversely affects living organisms as well as industrial products.