Groundwater originates as rainfall or snowmelt that seeps into the ground and fills pore spaces and fractures in rocks and sediments below the Earth's surface. It makes up about 1% of the water on Earth but over 35 times as much water as is contained in all lakes and streams. Groundwater occurs nearly everywhere and generally to depths less than around 750 meters. The global volume of groundwater is equivalent to a 55-meter thick layer spread over the entire planet. The occurrence and flow of groundwater is influenced by factors such as topography, climate, geology, and the properties of underground materials. There are four main sources of groundwater: connate water trapped during rock formation, rainfall, irrigation water, and tidal

1. GROUNDWATER
Introduction
Groundwater is a water that exists in the pore
spaces and fractures in rocks and sediments
beneath the Earth’s surface. It originates as
rainfall or snow, and then moves through the soil
and rock into the groundwater system, where it
eventually makes its way back to the surface
streams, lakes, or oceans.
Groundwater makes up about 1% of the water on
the Earth (most water is in oceans)

2. Introduction Cont.
But, groundwater makes up to 35 times
the amount of water in lakes and streams.
Groundwater occurs everywhere beneath
the Earth’s surface, but is usually
restricted to depth less than about 750
meters.
The volume of groundwater is equivalent
to a 55-meter thick layer spread out over
the entire surface of the Earth

3. Occurrence of Groundwater: Controlling factors
The occurrence of groundwater is influenced by the following
factors:
 Topography: A water table is not horizontal, but follows the
topography, or upward and downward tilts, of the land above
them. The water table is higher near the hilltops and lower near
the valleys, because water seepage into streams, swamps and
lakes cause lowering of water table near the valleys. In an
aquifer, the water table is mostly vertical and reflects the
surface relief of the area above. This is due to the capillary
effect of the soil, sediments and other porous material. In the
aquifer, the flow of groundwater is in both horizontal and
vertical directions and from points of higher pressure to lower
pressure. The slope of the water table is known as the hydraulic
gradient.

4.  Climate: In humid regions, recharge areas through which
water percolates underground are found everywhere except
streams, and adjacent floodplains. On the other hand, in arid
regions recharge areas encompass only the mountains and
adjoining alluvial fans and the streams below which porous
alluvium soil is there through which water can percolate and
recharge the groundwater. Groundwater is available at great
depth in dry or arid regions whereas it exists at shallow
depth in humid areas. Seasonally, water table rises during
the rainy season and sinks in the dry season. Change in
climate, for example, major increases in frequency and
intensity of exceptional rainfall events in groundwater
recharge areas can result in water tables rising to levels
higher than previously recorded maxima, causing extensive
‘groundwater flooding’ with damage to property and crops.

5.  Geology: This often determines the quantity of water that
filters below the zone of saturation, making the water table
easy to measure. Porous rocks can hold more water than
dense rocks. For example, an area underlain with pumice
which is a light and porous rock can retain a fuller aquifer, is
easier to assess than the water table of an area underlain with
hard granite or marble.
 Properties of Materials: The degree to which a body of
rock or sediments will function as a groundwater resource
depends on many properties. The two important physical
properties are porosity and hydraulic conductivity.
Transmissivity is also an important concept in knowing an
aquifer’s ability to yield groundwater.

6.  Porosity, which is the property of a rock possessing
pores or voids.
 Saturated and unsaturated zones.
 Permeability, which is the ease with which water can
flow through the rock.
 Aquifer, which is a geologic formation sufficiently
porous to store water and permeable enough to allow
water to flow through them in economic quantities.
 Storage coefficient, which is the volume of water that
an aquifer releases from or takes into storage per unit
surface area of aquifer per unit change in the
component of area normal to surface.

7. Sources Or Origin of Groundwater
There are four sources of groundwater:
 Connate water: It is the water which includes in the rock
itself, at the time of rock formation when water gets
trapped in rock strata. Because rock containing connate
water is typically formed from ocean sediments, it is
normal saline. In geology and sedimentology, connate
waters are liquid molecules which got trapped in the pores
of sedimentary rocks at their time of deposition. These
waters also contain many mineral components in the form
of ions in solution. The connate liquids are expelled as
rocks get buried and undergo lithification. If the escape
route for these fluids blocks, the pore fluid pressure builds
up in the rocks leading to overpressure.