Sources of water

The sources of natural water are Groundwater, surface water and Sea water

Ground water:-
Groundwater may be free as when directly fed through seepage from run off.Ground water may be confined. In this case it is separated from the soil surface by an impervious stratum.
Characteristics:-
The geological nature of the terrain determines the chemical composition of the held water. Water is constantly in contact with the ground in which it stagnates or circulates; an equilibrium develops between the composition of the soil and that of the water. Water which circulates in limestone contains bicarbonate alkalinity. Water that circulates in a sandy or granitic substratum has few minerals and isacidic.
The water is characterized by a weak turbidity, a constant temperature and chemical composition and a near absence of oxygen. It is often very pure microbiologically.
Potability:-
Groundwater may contain elements in concentrations that greatly exceed the standards for drinking water. Notable are iron, manganese, hydrogen sulphide and fluoride.A confined aquifer is less susceptible to accidental pollution than a free aquifer fed by the entire ground surface lying above it.Groundwater must be treated before distribution, whenever the concentration of one or several elements exceeds the limits authorised by regulations.

Surface Water:- 
This refers to all water on the surface of the ground both flowing and stored.t originates either from deep lying groundwater which feeds streams and rivers or from run-off. It can be found stored naturally as in lakes or artificially in storage reservoirs.
Characteristics:-
The chemical composition of surface water depends on the type of terrain the water has passed through before flowing into the drainage area water dissolves various components of the soil along its course. The exchange between water and air at the surface causes gases(oxygen, nitrogen, carbon dioxide) to dissolve in water.
Surface water is characterised by
• Presence of dissolved gases especially oxygen.
• Heavy concentration of suspended solids atleast in flowing water. In stored water, the large solids settle naturally and the remaining turbidity is, therefore colloidal.
• Presence of natural organic matter resulting from the decomposition of vegetable or animal organism living at the surface of the drainage area or in the river.
• Present of plankton.
• Daily and seasonal fluctuations of temperature, oxygen, iron, manganese, permanganate value, planston.
Potability:- 
Untreated surface water is rarely potable. Besides the contaminants mentioned above, it is usually polluted with bacteria. There may be also pollution from municiple wate water discharge, industrial effluents both organic and inorganic are fertilizers, pesticides, herbicides carried by rainwater and run-off

Sea Water:-                                                                                                                                         After utilising ground water and surface water, man has a third option of natural water in the oceans and seas flowing on the surface of the earth.
Characteristics:-
Sea water is characterised by a strong salinity that varies dependant on source. The salinity ranges from as low as 17 g/1 in the Baltic Sea to as high as 270 g/1 in the Dead Sea. The salinity in some of the other sources is as follows:

Source	Salinity g/l
Atlantic and Pacific Oceans	32 – 35
Mediterranean Sea	38 – 40
Red Sea	43 – 45

The physical characteristics of sea water that are important are suspended solids, turbidity, silt density index. These vary depending on location.Offshore, the suspended solids consist mainly of zooplankton and phytoplankton. Near the shore and near densely populated regions, pollution from municipal and industrial waste water can become excessive. The suspended solids level increase considerably.
For a typical chemical composition of sea water see below

Component	Unit	Value
pH		8.2 – 8.3
P Alkalinity	ppm CaCO3	0
M Alkalinity	ppm CaCO3	150
Equivalent Mineral Acidity	ppm CaCO3	30,850
Total Hardness	ppm CaCO3	6500
Carbonate Hardness	ppm CaCO3	150
Permanent Hardness	ppm CaCO3	6350
Calcium	ppm CaCO3	1100
Magnesium	ppm CaCO3	5400
Sodium	ppm CaCO3	24500

Ionic constituents of sea water.

Cations	Mg/1	Meq/1	Anions	Mg/1	Meq/1
Calcium	440	22	Bicarbonate	183	3
Magnesium	1315	108	Chloride	19880	560
Sodium	11040	480	Sulphate	2740	57
Potassium	390	10	Bromide	68	0.9
Strontium	1.3	0.3
Total Cations	13186.3	620.3	Total Anions	22871	620.9
TOTAL SALINITY 36.4 g/1

Potability                                                                                                                                    Sea water is not potable and must be treated to bring the constituents within the limits specified by local regulations.