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Source of Water Supply

Water moves in a cycle from earth to the air then to the earth again in a process known as the “hydrologic cycle”.This cycle is the ultimate source for all water resources. While on the earth, water for drinking comes from two sources: surface water from streams, rivers or lakes, and groundwater from underground aquifers. The rain that falls on the earth can be divided in to three parts: a) Infiltration b) Run off and c) Evaporation.Runoff and infiltration contribute to the augmentation of water resources on earth.

i. Ground Water

As the land surface is permeable, part of the precipitation or run off will infiltrate through the surface downwards. This infiltration water reaches the groundwater.The surface of this  e ground is known as the ground water table.This ground water table fluctuates up and down with the variation in rainfall and withdrawal of water from the nearby wells. When water from a well is being pumped out, the water from surrounding area flows into the well. The condition of groundwater and the knowledge geological formations of the area form basis for development of groundwater supply.

Water may be withdrawn from following ground water sources:

a) springs

b) infiltration galleries

c) porous pipe galleries

d) wells

In springs, the ground water reappears at the surface of earth depending on the geological formation in the area. The level of outlet of ground water at the surface will be lower than the ground water table level in the aquifer. Groundwater is generally pumped to the earth’s surface from wells. The water usually requires little treatment before its intended use because it was filtered through sand and rock as it settled into the earth.

ii. Surface Water
The water form the precipitation remaining after evaporation into atmosphere and infiltration into groundwater flows in the form of streams on earth surface and reaches surface water sources such as rivers and lakes. This water is generally more polluted than the groundwater due to their exposure to environment. Some additional treatment processes are usually needed for making this water suitable for different uses. If the water source is a river or stream, then the water is in flow and generally carries sand, silt and clay. Sedimentation, flocculation and filtration are strongly recommended for water from these sources. If the water is from stagnated sources such lakes and ponds, the sediments will not be there but the water is more prone to microbial contamination. Disinfection processes are more critical in water treatment schemes of such sources.

Whenever good quality water is available as a surface water, it should be used as source of water supply to save the cost of construction of well and pumping of ground water to earth surface. Surface water sources can be further classified as

a) streams

b) lakes

c) ponds

d) reservoirs

e) river and

f) rainwater harvesting system

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