Volume 5 Issue 6
Where Does Water Come From?
by Laurisa White Reyes
I have lived my entire life in the communities just north of Los Angeles, California and have traveled along Interstate 5 hundreds, perhaps thousands of times. As a young girl I always looked forward to that trip and seeing one particular spectacle along the way. Just beside the highway a massive concrete channel extends down the side of a mountain. Sometimes I would glimpse a deluge of rushing water beginning its turbulent journey from the top of the hillside down to the bottom where the currents disappeared from view. I did not know then what that impressive monument was, but the sight of thousands of gallons of water charging down the mountainside always left me awestruck.
Now, as an adult, I have learned that the edifice that impressed me so as a child is what is referred to as The Cascades. Like the tip of an iceberg, The Cascades are just a small segment of a 338 mile long series of channels and tunnels called The Los Angeles Aqueduct which provides nearly 500 million gallons of water each day to 3.7 million people in an area totaling 465 square miles. This aqueduct is a feat of engineering in that water flows its entire length at approx. 6,000 gallons per second powered solely by the force of gravity.
Why is this so amazing? As I lean over the kitchen sink I hold a glass in one hand and turn on the faucet with the other. The stream of water that pours out has traveled hundreds of miles before reaching my glass. It is something I have often taken for granted in the past. But now I ask myself a question that might normally come from the lips of my three year old. Where does water come from?
The Hydrologic Cycle
If my three year old were to ask me where water came from I would say it comes from the sky. It comes from rain. All water comes from precipitation – rain, snow, sleet, or hail – which can fall on mountain tops, collect in lakes, or soak into the ground. Moisture evaporates from the ocean surface and condenses into clouds. When these clouds cool, the moisture collects into droplets which then fall in the form of precipitation. When it rains, some of the water returns to the atmosphere via evaporation. The rest falls to the earth. Eventually all water returns to the ocean. This system is called the hydrologic cycle.
So where do we fit into this cycle? What is the source of the water we drink? Water that actually falls to earth, whether as rain or snow, eventually becomes available as a potential source for usable water. These sources are divided into two categories: surface water and ground water.
Precipitation that does not evaporate or soak into the ground but instead flows over the ground in the form of rivers or streams is called Direct Runoff. Most surface water accumulates as a result of direct runoff which drains into natural or artificial storage sites.
In some areas of the world where rainfall is scarce and where there may not be much groundwater, people use cisterns to store the water which drains from their roofs. This is one example of an artificial storage site. Examples of natural storage sites include rivers, streams, lakes, and reservoirs.
Water that percolates, or soaks into the ground, is either absorbed by plant roots or reaches a level where the earth is completely saturated with water, the aquifer. The upper surface of this saturated level is called the water table. In order for water beneath the ground to be used, it must be brought to the surface by means of seepage, wells, or springs.
In some areas the level of the water table is the same as certain surface water storage sites such as a lake or river. In this case, ground water seeps into and mixes with the surface water. Ground water can also be utilized by drilling a well and using a pump to extract the water, while water that flows naturally from the ground to the surface is called a spring.
Water Treatment Process
The method by which water is transported from its source (surface water or ground water) and delivered to the consumer is called a water supply system. Because surface water is exposed and is therefore accessible to contamination, it must be transported to a filtration plant where it undergoes a complex treatment process before being distributed to consumers (homes, businesses, or industrial sites.)
The Los Angeles Aqueduct, for example, transports water from the Mono Basin in the Sierra Nevada mountains (the source) until it reaches the filtration plant situated just below The Cascades. Here, water is treated before being distributed for consumer use. Below is a brief explanation of this process.
Screening: Water enters the plant by passing through a series of bar racks and rotating screens which remove leaves, rocks, and other debris. On one occasion employees found a live deer trapped against the racks at the entrance to the Los Angeles Aqueduct Filter Plant. They rescued the deer and released it into the wild.
Ozonation: After the initial screening, the water is injected with ozone which destroys bacteria and other living organisms and improves the taste, odor, and color of the water. Any unused ozone is collected, converted back to oxygen, and released into the atmosphere.
Rapid Mixing: Following ozonation, the water enters rapid mixers where chemicals are added to remove turbidity, or cloudiness. These chemicals react with fine particles in the water and prepares them for the next step.
Flocculation: This is a slow stirring process that allows the small particles which cause turbidity to cluster together so they can be more easily removed.
Filtration: After flocculation the water flows into filter beds, large concrete boxes containing deep layers of crushed anthracite coal over a thin gravel base. The water flows through these layers which trap the particle clusters leaving the water clean and clear.
Chlorination: This is the final step of the treatment process. Chlorine is added to insure lasting disinfection.
(Note: Not every city treats their water in exactly the same fashion. Well water is commonly treated only with chlorine while water taken from lakes or rivers is treated with a more complex process. For more information on the process used in your community, contact your local water agency. Also, many water districts host open houses or offer tours of their treatment plants.)
Once water is retrieved from its source and treated at a filtration plant, it is ready to be distributed to consumers by way of the distribution system which consists of storage facilities, pumping stations, pipes, meters, valves, etc.
A storage facility is a structure, usually a reservoir or elevated tank, in which treated water is stored before being distributed to consumers. Reservoirs and elevated tanks differ greatly. Reservoirs are located at ground level and have a large surface area, similar to a small lake. Reservoirs are commonly used in mountainous regions. Elevated tanks are erected high above ground level and are often used in communities where the land is relatively flat, such as in the mid-west.
While some water systems rely completely on gravity to distribute their water, most communities must do some pumping to accomplish this. Pumps are used to increase water pressure and aid in the transportation of water which must travel through a series of pipes before reaching the consumer. Pipes can be made out of steel, iron, concrete, copper, brass, or plastic and vary in size from ˝ inch to several feet in diameter. Concrete pipes can be as large as 240 inches in diameter. Valves and meters are used to help regulate and measure the flow of water through the pipes.
At the end of the line I stand with my glass poised beneath the kitchen faucet. With a simple turn of a knob, a stream of cool, clear water pours out and I envision the water tumbling down The Cascades. A few years ago, The Los Angeles Department of Water and Power installed colored fiberoptic lights at The Cascades so now whenever I drive by there at night, the water shifts from red to blue, to lavender, to green, and back to red again. It is even more beautiful now than when I was a child. But now it is more than just an breathtaking image to me. It represents the long, arduous journey each drop of water must make to reach my thirsty lips and I am more than awestruck. I am grateful.
Activities and Resources
Ocean water evaporates at a rate of about six feet per year. Children can learn to understand the principles of evaporation using the following experiment.
3 Containers with very different amounts of surface area (ie. a bowl, a cup,
1. Using the quart jar, fill the containers with
equal amounts of water. Record the amount on the paper. (Use the ruler to measure
the amount of water while in the quart jar.)
www.state.fl.us/citytlh/water/water.html This site from the Tallahassee, Florida water agency has a great program for determining how much water is wasted by a leaky faucet.
www.ladwp.com/water/supply/index.htm Learn more about the Los Angeles Aqueduct and the largest water distribution system in the country.
www.epa.gov/OGWDW/kids A great site about water conservation for kids. Includes an extensive list of experiments and projects to try at home.
www.water.usgs.gov/education.html An educational web site all about water.Copyright © 2006 Modern Media