Water cycle | Hydrological cycle | Movement of water between the atmosphere, land, and oceans|

The water cycle, also known as the hydrological cycle, is the continuous process of water circulation on Earth. It involves the movement of water through various stages, changing between different states of liquid, gas, and solid; and moving between the atmosphere, land, and oceans. This biogeochemical cycle is responsible for maintaining weather conditions.
The water moves from one reservoir to another, such as from river to ocean, or from the ocean to the atmosphere, by the physical processes of evaporation, condensation, precipitation, infiltration, surface runoff, subsurface flow, transpiration, melting and sublimation.
The water cycle is a fundamental process that plays a critical role in sustaining life on the planet earth. 97% of the world’s water is stored within the oceans. Of the ocean water, a very small proportion becomes frozen at it reaches the poles and is stored as ice within glaciers.
Evaporation: The water cycle is powered from the energy emitted by the sun. This energy heats water in the ocean and seas. Water evaporates as water vapor into the air. So, the water cycle begins with the process of evaporation, where solar energy from the sun heats up bodies of water (oceans, lakes, rivers, and even moist soil). This heat causes water molecules to gain energy and transform from the liquid state into water vapor (a gas). Water vapor is less dense than liquid water, so it rises into the atmosphere. Some ice and snow sublimates directly into water vapor.
Condensation: As water vapor rises higher in the atmosphere, it cools down due to lower temperatures at higher altitudes. This cooling causes the water vapor to lose energy and change back into tiny water droplets, forming clouds. Condensation is the process of converting water vapor into liquid water. A huge concentration of these droplets over a large area in the atmosphere becomes visible as cloud, while condensation near ground level is referred to as fog.
Precipitation: As the clouds are moved around the earth’s atmosphere they collide and grow. Eventually the water droplets grow large enough so that they are heavy enough to fall as precipitation (rain) or as snow, hails etc. and can accumulate in ice caps and glaciers. The water is used by planta and can be consumed by animals, who cycle the water through their bodies.
Runoff and infiltration: Once precipitation reaches the Earth's surface, it follows two primary pathways. Some of the water is absorbed by the soil through a process called infiltration. Infiltrated water may be taken up by plant roots or percolate down to recharge groundwater reservoirs. The rest of the water, known as runoff, flows over the surface of the land, eventually making its way into streams, rivers, and, ultimately, into the oceans. Some of the water that makes it to the ground is affected by gravity and flows back into the ocean via surface runoff. Furthermore, some of this water joins with freshwater streams and rivers, which eventually lead to the oceans, or it may be stored within lakes and reservoirs. This freshwater can be consumed by animals, who cycle the water through their bodies.
Ground Water flow: A portion of the infiltrated water becomes groundwater, which moves slowly through permeable rock layers called aquifers. Groundwater flow plays a crucial role in sustaining baseflow in rivers and providing a reliable water supply for wells and springs. Much of the water that fell as rain, soaks into the ground through infiltration. Here it either infiltrates deep into the rock, and forms huge stores called aquifers or it remains relatively close to the surface as groundwater flow. Some of the groundwater emerges from springs and surface water bodies, eventually making its way back to the ocean. The groundwater is taken in by the roots of plants and is used for photosynthesis.
Transpiration: Transpiration is the process through which water moves from plants into the atmosphere. Plants absorb water through their roots and release water vapor through small pores called stomata in their leaves. This water vapor then becomes part of the atmosphere and can later condense to form clouds.
Sublimation and Melting: In some cases, water can transition directly between its solid (ice) and gaseous (water vapor) states without passing through the liquid phase. This process is called sublimation, which occurs when ice or snow turns into water vapor under specific conditions. On the other hand, when ice melts, it becomes liquid water, and this process is known as melting.