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The Hydrological Cycle

The Water Cycle

The Path to Clean Water

The Water Cycle Components

Similar to our Path to Clean Water™ graphic, the water cycle is a circle.  Like any circle, you can start anywhere and end where you began. In the water cycle, water is recirculated through the process of removing impurities in the water.

The major components of the water cycle rely on the following processes: Evaporation/Transpiration, Advection, Precipitation, Infiltration/Percolation, Direct Runoff, Aquifer Recharge, and Surface Water and our Stream Networks.   The water cycle for the Planet is powered by the Sun and natural geological forces of the planet.

Did You Know that, "Asteroids, not comets, may have delivered most of Earth's water to the planet when the solar system was young" (Source). Those asteroids were responsible for creating our vast oceans.

The oceans of our Big Blue Ball are a good place to start the cycle and water evaporation

Let us start with the Ocean and Water that is Evaporating from the Ocean.


Evapotranspiration is the combined net effect of two processes: evaporation and transpiration. Evaporation is the process of returning moisture to the atmosphere. Water on any surface, especially the surfaces of ponds, streams, rivers, lakes, and oceans, is warmed by the sun's heat until it reaches the point at which water turns into the vapor, or gaseous, form. The water vapor then rises into the atmosphere. Evaporation typically accounts for a significant volume of water directly returned to the atmosphere.

Transpiration is the process by which plants return moisture to the air. Plants take up water through their roots and then lose some of the water through pores (stomata) in the underside of their leaves. As air passes over the surface of the leaves, the water evaporates into the air.


There is a net movement of water vapor in the air above oceans to air above the land. This horizontal movement of moist air is advection. Water moves from continental areas into oceans by surface flow and baseflow. That movement is balanced by the advection of moist air from over ocean areas to the continents, followed by precipitation. Dry areas and even deserts are found downwind of where mountains impede the advection of moist air inland (the orographic effect).


Condensation is the cooling of water vapor until it becomes a liquid. As the dew point (the temperature at which air becomes completely saturated with water vapor) is reached, water vapor in the air forms tiny visible water droplets. When these droplets (or ice crystals if the air is cold enough) form in the sky and other atmospheric conditions are present, clouds will form. As the droplets collide, they merge and form larger droplets and, eventually, precipitation may occur.

Precipitation is moisture that falls from the atmosphere as rain, snow, sleet, or hail. Precipitation varies in amount, intensity, and form by season and geographic location. These factors impact whether water will flow into streams or infiltrate into the ground. In most parts of the world, records are kept of snow and rainfall. This allows scientists to determine average rainfalls for a location as well as classify rainstorms based on duration, intensity, and average return period. This information is crucial for crop management as well as the engineering design of water control structures and flood control.


Infiltration is the entry of water into the soil surface. Infiltration constitutes the sole source of water to sustain the growth of vegetation and it helps to sustain the groundwater supply to wells, springs, and streams. The rate of infiltration is influenced by the physical characteristics of the soil, soil cover (i.e. plants), water content of the soil, soil temperature, and rainfall intensity. The terms infiltration and percolation are often incorrectly used interchangeably.

Percolation is the downward movement of water through rock. Percolation occurs beneath the root zone. Groundwater infiltrates through the soil much as water fills a sponge, and percolates from space to space along fractures in rock, through sand and gravel, or through channels in formations such as cavernous limestone.

Direct Runoff

Direct runoff is that portion of the water that does not infiltrate or percolate into soil and rock to recharge the groundwater aquifer and is typically the portion of the precipitation that immediately runs off impervious or saturated surfaces into local gullies, creeks, wetlands, rivers, bays, and even the ocean.

Groundwater Recharge / Groundwater Aquifer

A significant amount of the water that infiltrates and percolates into the ground ultimately becomes part of the groundwater flow system and the aquifer. Because it may take decades to thousands of years for this water to ultimately move back out from the ground into our local creeks, springs, streams, rivers, and the ocean, I like to think of this groundwater storage as our Water Bank. It is critical that we make sure that there is more water going into this groundwater bank than we try to take out with water wells. Please remember - Groundwater Recharge occurs mostly in the "RECHARGE Zone.”

Creeks, Springs, Streams, Rivers, and the Ocean

When it is in the middle of a hot summer or very cold winter with no rainfall and everything is frozen and your local stream is flowing, this is because groundwater is coming out of storage in the ground to support the baseflow or low-flow of the stream. Therefore, many of our streams, springs, creeks, wetlands, and even the ocean are located within groundwater "DISCHARGE Zones.” Groundwater discharge to these zones is critical in maintaining the health of the ecosystem. In some cases, such as a losing stream or wetland that is located in the headwaters of a watershed, streams and wetlands can also be part of the "Recharge Zone.” To put it another way, a recharge zone is where there is a net movement of surface water into the ground as opposed to a discharge zone where there is a net movement of water from the ground back to the surface or a surface body of water.

Guess what?  We end up back at the Ocean.

Please Remember

Humans do not control the planet, but we can disrupt or alter the natural cycles. In my opinion, we have a tendency to want to make the system go faster than the normal cycles would permit and we have a tendency to build and rebuild in the wrong places. Flooding of streams, creeks, and wetland areas is a natural process and Erosion is a natural process, but sometimes we take actions that make these conditions worse by building in the wrong areas, adding dikes and levees, and thinking that we control the water cycle.

We are part of the water cycle, "We DO NOT Control IT- It Controls US! "

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