Sources of water and water quality parameters

SOURCES OF WATER

Sources of water are

• Surface water sources: ponds, lakes, streams, rivers
• Ground water sources: Dug wells, Bore wells, Infiltration wells and Infiltration galleries

WATER QUALITY PARAMETERS

The following are the important parameters of water for domestic use:

• Water must be colourless and sparkling clear
• Water must be free from suspended solids and must not deposit sediments in resting condition
• Water should have an acceptable taste free from odour
• It should be reasonably soft
• It should be available in plenty
• It should be free from disease producing bacteria
• It should be free from objectionable dissolved gasses
• It should have sufficient quantity of dissolved oxygen
• It should be free from harmful salts
• It should be free from objectionable minerals like Iron, Manganese, Lead, Arsenic and other poisonous metals
• It should be free from radioactive substances like radium, strontium, etc
• It should not contain phenolic compounds, chlorides, fluorine and iodine
• It should not lead to scale formation and should not be corrosive

Standards of potable water

The following physical and chemical standards for potable water given by Ministry of Urban Development, India are:
Physical characteristics

• Turbidity is caused due to presence of suspended and colloidal matter in water. Groundwater is less turbid than surface water. Turbidity is a measure of resistance of water to the passage of light through it. Turbidity is measured using nephelometry which involves measurement of light scattered by particles at right angles to the incident light beam. The amount of scattered light is proportional to the concentration of particles in the sample. It is expressed as Nephelometric Turbidity Unit (NTU). The acceptable value for turbidity according to IS (Indian Standards) is 10 - 25 NTU

•  Dissolved organic matter from decaying vegetation or some inorganic materials imparts colour to water. It is measured by comparing colour of water sample with standard solutions of different colour intensities. Standard unit of colour is produced by 1mg of platinum cobalt dissolved in one liter of distilled water (Platinum cobalt scale). The acceptable colour value of treated water is 5-25 cobalt units.

•  Taste and odour is imparted to water mostly due to organic chemicals and partly due to inorganic chemicals. Taste and odour are expressed in terms of odour intensity or threshold values. Flavor Profile Analysis (FPA) is a new method to estimate the taste of water sample and is based on flavor. The character and intensity of taste and odour indicate the nature of pollution and the presence of microorganisms.
• Temperature of water that is ideal for drinking is between 5 and 12∘C. Above 25∘C water is not recommended for drinking.

Chemical characteristics

• pH is the negative logarithm of hydrogen ion concentration and is expressed on a scale of 0 to 14. It denotes if the water is acidic or basic. Lower number indicating that the water is acidic and higher number indicating that the water is alkaline. The recommended pH range for treated water is 6.5 to 8.5
• Acidity of water is a measure of its capacity to neutralise bases. It represents carbondioxide or carbonic acid. Acidity of water may be caused by uncombined carbondioxide, mineral acids and salts of strong acids and weak bases. Acidity is expressed as mg/L in terms of Calcium Carbonate
• Alkalinity is a measure of its capacity to neutralise acids. It is expressed as mg/L of Calcium Carbonate.The various forms of alkalinity are hydroxide alkalinity (OH⁻), carbonate alkalinity (CO₃⁻⁻)
• If water consumes excessive soap to produce lather, it is said to be hard. Hardness is caused due to divalent metallic cations. The main hardness causing cations are Ca, Mg, Sr, Md and Fe ions. The associated anions with these cations are sulfates, carbonates, bicarbonates, chlorides and nitrates. Total hardness of water is the sum of calcium and magnesium concentrations, both expressed as calcium carbonate in mg/L. Hardness may be temporary (due to carbonates and bicarbonates) which can be removed by boiling or permanent hardness which cannot be removed by boiling. The IS acceptable value for total Hardness as CaCo3 (mg/l) is 300 mg/L.
• Chlorides (as Cl in mg/l) - 200
• Sulphates (as SO4 in mg/l) - 200
• Fluorides (as F in mg/l) - 1.0
• Nitrates (as NO3 in mg/l) - 45
• Calcium (as Ca in mg/l) - 75
• Magnesium (as mg in mg/l) - Not more than 30
• Iron (as Fe in mg/l) - 0.1
• Manganese (as Mn in mg/l) - 0.05
• Copper (as Cu in mg/l) - 0.05
• Zinc (as Zn in mg/l) - 5.0
• Phenolic compounds (as phenol in mg/l) - 0.001

• Anionic detergents  (as MBAS in mg/l) - 0.2
• Mineral oil (in mg/l) - 0.01

Toxic metals

• Arsenic (as As in mg/l) - 0.05
• Cadmium (as Cd in mg/l) - 0.01
• Chromium as hexavalent chromium                                          - 0.05
• (as hexavalent Chromium in mg/l)
• Cyanides (as CN in mg/l) - 0.05
• Lead (as Pb in mg/l) - 0.1
• Selenium (as Se in mg/l) - 0.01
• Mercury (Total Hg in mg/l) - 0.001
• Polycyclic Aromatic 
• Hydrocarbons (PAH in mug/l) - 0.2
• Radioactivity
• Gross alpha activity -3 pico curie/l
• Gross beta activity                                                                       - 30 pico curie/l