Prehistoric Arrival

Water arrived on our planet when it was young, as giant snowballs from space that crashed to the surface and sent trillions of gallons of steam boiling through the atmosphere. When it finally cooled it turned to rain and collected on the surface. Most of this seeped into rocky crevasses and disappeared beneath the surface. When the planet had its fill, the water pooled on top and formed the oceans as we know them today. Indeed, there is more water inside the Earth than there is on top of it!

The Water Cycle Begins

Over billions of years the water dissolved the rocks around it and turned very salty and unfit for most organisms to drink. Luckily, we live close enough to our local star the Sun for it to warm up the oceans until the water, but not the salt, evaporates, sending freshwater on a long adventure. Just as luckily, we don’t live too close to the Sun like Mercury, where it is so hot that water only exists as steam.  On our planet the water eventually cools, for example when clouds are forced by wind up the chilly slopes of a mountain.

Now the water condenses, turning from gas back into a liquid, and falls to Earth as rain and soaks into the soil. The water that does not soak too deep flows downhill, collecting in streams and lakes. Eventually, all this flowing water returns to the lowest spot, the Ocean, where it mixes with the salty water and goes through the cycle all over again.

Fresh Water for Everyone

The water that sticks around longer has a chance to nourish plants, animals, and humans. Thirsty roots under the Island’s forests of Fir and Cedar trees absorb this water and send it up the trunk, where it keeps the wood alive and the leaves bright green. The water evaporates from millions of little holes in the leaves called stomata, returning to the atmosphere. In this way, forests keep freshwater cycling nearby and more available for all the life that depends on them.


Water that escapes the thick roots but doesn’t flow too fast downhill collects in underground lakes. Here in the Islands we can access these sources if we dig a hole down a few hundred feet, and can then pump the water back up for drinking. As long as the rain soaks into the ground fast enough to recharge the water we take from this lake, the cycle continues as usual. If we take too much, the water falls deeper underground and we have to dig deeper to find it. Also, ocean water surrounding our Islands mixes with the fresh water below the surface, turning it saltier. But as long as we take only what we need, the planet will do the rest for us!


What is a Watershed?

A watershed can be defined as “the entire body of land that drains water, sediment, and dissolved materials to a common outlet, such as a stream, river, or other body of water” (USDA 1993).

Watershed land areas are bounded by ridges in topography that determine which way water will flow. Activities taking place within the watershed, whether it is on the land or in water or in the air, all have the potential to affect the watershed system.

Water circulates in various forms through the environment in a process called hydrologic cycle. Through the hydrologic cycle powered by the sun’s energy, water molecules are recycled from the land, to the air, and back to the land.

Water is put into the atmosphere by evaporation and through transpiration by plants and trees. This atmosphere vapor is transported by winds, condensed into clouds, and then returned by gravity back to the earth’s surface as precipitation, rain or snow.

When precipitation falls on the landscape of a watershed, the water may take one of four paths to reach an outlet. Depending on factors such as climate, shape of the watershed, slope, orientation, soil geology, and vegetative cover, water may evaporate directly back unto the air; flow over land to a pond or stream or larger body of water as runoff; soak into the ground to be absorbed by plants and trees for evapotranspiration; or seep into the groundwater .

Tip:  The “natural system’s” ability to filter out pollutants is greatly affected by land use.  Maintaining vegetative cover increases the natural system’s ability to filter pollutants.


The quantity and quality of water produced from a watershed is greatly affected by its soils, vegetation, and the human activities taking place within the watershed’s boundaries. As water flows over land, into lakes or other larger bodies of water and through soils, pollutants like oil, bacteria, nutrients, sediment and chemicals can be taken up or filtered out. When rain hits pavement or rooftops, instead of soaking into the ground and flowing gradually to the stream or lake or larger bodies of water, it is carried immediately to the nearest ditch or storm sewer and then into the steam or lake or other larger bodies of water. The concentration of impurities, the speed and amountof water, topography of the land, the type of soil and material the water flows over or through, and the distance the water travels all contribute to determining the effect the “natural system” has on filtering out the impurities to maintain good water quality.

Tip: Working together, citizens can increase awareness of the importance of water quality and make a positive impact on our future.


Our Local Watersheds 

Rain that falls on the Islands flows to the Salish Sea guided by the hills and valleys. These boundaries define watersheds, areas where all the rain drains to the same body of water. The largest watershed in the Islands is the False Bay Watershed, which drains San Juan Valley and Beaverton Valley into False Bay. Along the way, this water picks up nutrients and chemicals from the watershed landscape and carries them to the shore.




  • Evaporation is when the sun evaporates water from seas and land and converts it to vapor or gas which ascends into the atmosphere. Water vapors can condense as fog or mist but mostly it collects to form clouds.
  • Precipitation occurs when clouds become soaked with water vapor. Water falls to the Earth as rain, hail or snow. Not all of the precipitation in the sky will reach the earth; some will evaporate between the sky and the land and go back into the water cycle.
  • Transpiration is when water infiltrates the soil and the roots of plants and trees, and “transpires” through their leaves. This process allows plants to use the sun’s energy water and minerals to create nutrients. The water vapor is a by-product of photosynthesis. Lots of plants in one area such as in a rain forest transpire and cause humidity to rise. High levels of this moisture return to the atmosphere as vapor.
  • Infiltration is the process where water is filtered through subsurface rocks or soil, and collects in aquifers and underground streams. Later this water can be pumped out of the ground for our use, such as in a well or irrigation system. Water that reaches the earth either becomes runoff across the land, collecting into a body of water, or infiltrates into soil that collects underground.
  • Combustion is caused when automobile motors and engines release water vapor into the atmosphere. This vapor can be water or a waste product. The waste product contains high concentrations of sulfur and nitrogen oxides and can form sulfuric and nitric acids that fall to earth, known as “acid rain”.
  • Respiration occurs when animals and humans breathe and their lungs release water vapors into the atmosphere that are retained in their lungs.



© San Juan Islands Conservation District 2016