Do you remember learning about the water cycle in elementary school or junior high school? It would have been introduced in the third grade and every year through the eighth grade. Unless you’re a water cycle fanatic or work in the water industry, the chance is junior high school was the last time you even thought about the water cycle. 

So, let’s take a stroll down memory lane with a water cycle refresher. 

The water cycle is the path that all water follows as it moves around Earth in three different states: liquid, solid and gas. 

Liquid water is found in oceans, rivers, lakes and underground. Solid ice is found in glaciers, snow, and at the North and South Poles. Water vapor is a gas found in the Earth’s atmosphere.

About 75 percent of our planet is covered by water or ice. The water cycle is the endless process that connects all that water. It connects the Earth’s oceans, land, and atmosphere.

According to the United States Geological Survey (USGS), 71 percent of the Earth’s surface is covered in water. The oceans hold about 96.5 percent of the water on Earth. 

About 1.7 percent of Earth’s water is stored in polar ice caps and glaciers. Rivers, lakes, and soil hold approximately 1.7 percent. A tiny fraction, just 0.001 percent, exists in the Earth’s atmosphere as water vapor.

The water cycle involves the continuous circulation of water in Earth’s atmosphere as it flows between storages. It can be broken down into nine steps.

• Evaporation: Water from Earth’s surface turns into vapor from the heat of the sun and travels to the atmosphere.
• Condensation: Once the water is turned to vapor, it rises into the atmosphere; the higher up it goes, the cooler it gets. The cold temperatures condense the vapor into droplets that form clouds and fog.
• Sublimation: A process that also forms water vapor. Ice in freezing areas turns the water into vapor without the liquid phase. Varying temperatures and pressure typically cause sublimation; the temperature must be low or the pressure high. This process takes much longer than evaporation.
• Precipitation: The clouds of vapor release the water after condensation. Smaller water particles combine and form drops of rain.
• Transpiration: Like evaporation, this step of the water cycle forms water vapor. Water drops are absorbed by the soil and then used by plants during photosynthesis. Plants absorb the water, using the hydrogen from the water and carbon dioxide from the air to create oxygen.
• Surface runoff: When water lands on the surface of the Earth, it runs off down landscapes because of gravity; this is called runoff. This runoff water helps transport minerals and impurities. These runoff streams connect with others to form channels, returning the water to lakes, rivers and oceans.
• Infiltration: Happens when surface runoff does not return to a large body of water like a lake, river or ocean. The water is instead absorbed by the soil and becomes groundwater. The water filters through the ground and becomes pure water.
• Plant uptake: Plants need water to grow and maintain structure, they also help absorb groundwater via their root systems. The water they absorb travels to their leaves, where this water evaporates, contributing to how much water vapor is in the air.
• Evapotranspiration: Includes all processes of evaporation from the land (soil and other surfaces) and transpiration from plants.

Rainfall over the land surface follows various routes in its subsequent paths. Some of it evaporates, returning to the atmosphere; some seeps into the ground as soil moisture or groundwater; and some runs off into rivers and streams. 

Precipitation is a key piece of the water cycle that’s needed to ease drought conditions. Rain causes surface runoff and runoff sends the water underground or through streams and rivers that feed into reservoirs and eventually the ocean. 

The more saturated the ground is, the more surface runoff will be generated. This piece of the water cycle helps to increase our reservoir levels. If the ground is dry when precipitation occurs, more infiltration and plant uptake will take place, which helps to regenerate plant growth and gives our depleted landscape some help. 

The water cycle is a continuous process and has no beginning or end. It is the path that all water follows as it moves around Earth in different states. To learn more about the water cycle and how the National Aeronautics and Space Administration (NASA) is observing it through satellite data collection, visit here.