The process by which water on the ground surface seeps into the soil is called:

Infiltration is the process by which water on the ground surface, from rain, melting snow or irrigation, enters the soil. It is an important part of the water cycle (hydrological cycle), because it replenishes soil moisture, which plants use, and recharges groundwater.

The rate at which water enters the soil is called the infiltration rate. It depends on several factors:

Soil texture: sandy soils have large pores and allow quick infiltration, while clay soils have tiny pores and allow slow infiltration.

Soil moisture: dry soil absorbs water faster than wet, saturated soil.

Vegetation cover: plant roots and organic matter make the soil porous and slow down surface runoff, increasing infiltration.

Land slope: water runs off quickly from steep slopes, leaving less time to soak in.

Rainfall intensity: very heavy rain may exceed the infiltration capacity, causing runoff and floods.

Land use: paved surfaces in cities, such as roads and buildings, prevent infiltration and increase urban flooding.

Once water has entered the soil, its further downward movement through the soil and rock layers to the zone of saturation (groundwater) is called percolation. So infiltration is the entry of water into the soil surface, and percolation is the movement of water deeper down.

The water cycle involves several processes:

• Evaporation: water turns into vapour from oceans, lakes and rivers.
• Transpiration: plants release water vapour through their leaves; together with evaporation, this is called evapotranspiration.
• Condensation: water vapour cools and forms clouds.
• Precipitation: water falls as rain, snow or hail.
• Runoff: water flows over the surface into streams and rivers.
• Infiltration and percolation: water enters the ground.

Water conservation methods such as check dams, contour bunding, rainwater harvesting and afforestation increase infiltration and groundwater recharge. The Jal Shakti Abhiyan "Catch the Rain" campaign promotes these.

Why not the other options?

• ✗Percolation is the downward movement of water through soil layers to the groundwater.
• ✗Transpiration is the loss of water vapour from plants.
• ✗Evaporation is the change of liquid water into vapour.