Groundwater refers to the water present beneath the Earth’s surface. It constitutes approximately 0.6% of the planet’s total water reserves.

Sources of Groundwater

Infiltration of rainwater into the ground.

• Seepage from rivers into the subsurface.
• Water trapped during the Earth’s crust formation.
• Cooling and condensation of gases and steam from igneous activities.

Components of Groundwater

1. Unsaturated Zone:
   • Located directly below the surface, this zone is also called the vadose or aeration zone.
   • Here, the spaces in rocks are partially filled with water and partially with air.
2. Saturated Zone:
   • Found below the unsaturated zone, this area has all its pores and rock fractures filled with water.

1. Water Table: 
   • The upper limit of the saturated zone is known as the water table.
2. Aquifers:
   • These are underground reservoirs where water collects. The movement of water stops when it reaches impermeable rock layers.
   • Aquifers often contain enough water for uses such as drinking, irrigation, and industrial processes.
3. Aquicludes:
   • These are layers of rock, such as clay and shale, that are impermeable and restrict the flow of groundwater.
4. Porosity:
   • Refers to the amount of empty space within a material, known as pores, which can store fluids. Rock porosity determines its capacity to hold water.
5. Permeability:
   • Measures how easily fluids can pass through a material.
   • High permeability indicates well-connected pores, while low permeability signifies isolated pores.
   • Examples: Pebble, gravel, and sand are permeable, whereas clay is impermeable.

Wells and Artesian Wells

Wells
Wells are man-made structures drilled into the ground to extract groundwater.

Types of Wells

• Permanent Wells: Reach the permanent water table and provide water year-round.
• Intermittent Wells: Reach only the temporary water table and contain water primarily during the rainy season.

Artesian Wells

• These wells release water naturally, like a fountain, due to hydraulic pressure.
• Found in areas with a saucer-shaped synclinal structure where a permeable rock layer is sandwiched between impermeable layers.

• Examples: New South Wales (Australia), Kansas (USA), and the Tarai region (India).
• Formation Process: Rainwater enters the exposed ends of the permeable layer, saturating it. When a well is dug, water is forced upward by pressure.

Springs

A spring is a natural flow of water emerging from the ground, formed under various geological conditions.

Types of Springs

1. Perennial Springs: Flow continuously throughout the year.
2. Intermittent Springs: Flow ceases at times due to limited water supply.
3. Hot Springs: Release hot water heated by magma beneath the Earth’s surface.
   • Examples: Sakhalin Island (Russia), Rajgir (Jharkhand), and Bakreshwar (West Bengal, India).
4. Geysers: Intermittent hot springs that eject water and steam at regular intervals.
   • Difference from Hot Springs: Geysers have intermittent eruptions, while hot springs have continuous water flow.
   • Examples: Old Faithful Geyser (USA).
5. Scarp-Foot Springs: Occur along the fault lines where rock layers meet, often forming a “spring line” of water flow.
6. Vauclusian Springs: Found in limestone regions where water enters underground cavities and re-emerges as fountains.
   • Example: Fountain de Vaucluse (France).