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1.8: Water Supply

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    We have already discussed our water supply in several chapters. Remember, the two main sources of supply for use are surface water supplies and groundwater supplies. And, as you will see in Chapter 10 there are other sources of water used to supplement these two main sources. If you recall, surface water receives its supply from precipitation in the form of rain, sleet, snow, etc. Moist warm air rises and condenses on upward slopes. On the west coast, rain falls mostly on the westward facing mountains and as dry air drops a rain shadow effect occurs on the east facing slopes. Much of this precipitation runs off into streams, rivers, and lakes. Evaporation occurs condensing water back into the atmosphere. Some of it percolates into the ground and becomes groundwater. Plant roots also take up some water and transpiration occurs. The process of water transpiring and evaporating back into the atmosphere is referred to as evapotranspiration. When precipitation occurs the entire cycle is continued. This cycle is known as the hydrologic cycle.

    Most of the water on earth is salt water. In fact 97% of the earth’s water is seawater and only 3% is fresh water. This means of all the water on the planet, we get our fresh water from 3% of it. The story continues. Approximately 69% of all fresh water is in the form of glaciers and icecaps. Groundwater is approximately 30% and surface water is less than 1%. This is fairly startling considering much of the water we use every day comes from a fraction of the fresh water on earth. The vast majority of this small fraction is found in lakes. Some of these lakes are natural and some are manmade storage reservoirs behind dams. Much of the water that supplies California sits in these “manmade” storage reservoirs as the water moves through several aqueduct systems.

    California Surface Water

    California’s diverse climate and geography presents an interesting situation when it comes to water supply. Approximately 2/3 of the state’s rainfall occurs in the upper 1/3 of the state, while 2/3 of the usage occurs in the lower 1/3 of the state. In other words, water is used more in areas where it doesn’t naturally fall from the sky. Therefore, surface water supplies are plumbed thousands of miles across California. There are 6 main aqueduct systems providing surface water throughout the state. They include:

    • State Water Project
    • L.A. Aqueduct
    • Colorado River Project
    • Hetch Hetchy Aqueduct
    • Mokelumne Aqueduct

    These aqueduct systems originate in the central to northern portion of the state and are operated by a variety of agencies.

    State Water Project

    The California State Water Project (SWP) originates from the tributaries of Lake Oroville, north of Sacramento. It runs a distance of approximately 600 miles and includes twenty-nine (29) dams/storage reservoirs, eighteen (18) pumping plants and five (5) hydroelectric power plants. It passes through the California Bay Delta. The Bay Delta is one of the nation’s largest and most complex water delivery system and is known for its agricultural productivity, ecological diversity, and complexity. The SWP also includes the world’s largest water lift. The Edmonston Pumping Plant at the base of the Tehachapi Mountains pumps (lifts) water 2,000 feet over this mountain range. More than 2/3 of Californians receive water through the SWP. The California Department of Water Resources (DWR) operates the State Water Project.

    Los Angeles Aqueduct

    In contrast, the Los Angeles Aqueduct is owned and operated by the Los Angeles Department of Water and Power. In the early 1900s, William Mulholland and Fred Eaton traveled north to find additional sources of supply for Los Angeles. What they discovered was the Owen’s Valley, which had more water than the area knew what to do with. They built an aqueduct approximately 223 miles from the Valley diverting water down to Los Angeles. The unique thing about this aqueduct system is it flows entirely by gravity. The book and movie titled Cadillac Desert documents the vast undertaking by William Mulholland.

    Colorado River Aqueduct

    The Colorado River Aqueduct begins at Parker Dam along the Colorado River and travels approximately 242 miles west into California. There are two (2) storage reservoirs along the way and five (5) pumping stations to traverse the desert. The Metropolitan Water District of Southern California holds the priority water rights on the Colorado River Aqueduct.


    Underground aquifers hold a vast amount of water. Pores in the soil and fractures in rock formations hold millions of gallons of water beneath the earth’s surface. As rain falls and snow melts, rivers fill with water and recharge these underground storage basins. There are three (3) main types of aquifers, each with unique geological characteristics. An unconfined aquifer can be very shallow, around 20 feet below the earth’s surface to several hundred feet deep. These aquifers are commonly made of alluvium deposits consisting of porous, water-bearing materials of sand and gravel. These aquifers are capable of yielding large amounts of water and relying on annual recharge to keep them full of water. Beneath unconfined aquifers are confined aquifers. These aquifers are separated by an impermeable layer of soil (commonly clay) with porous sand and gravel beneath the clay. This impermeable layer acts as a barrier between the soil sediments above acting as a protective shield. Confined aquifers are less susceptible to surface contamination because of this impermeable layer. Fractured rock aquifers are not very common, but they can exist in mountain regions where there are cracks or fissures in the underlying rock. Water from precipitation can then make its way into the cracks and can be withdrawn by wells. Most wells require a pump and motor to get the water from below the ground to the surface. However, where recharge zones are higher than the elevation, the water can flow out without any help. These types of aquifers are referred to as artesian.

    Groundwater banking or aquifer storage and recovery (ASR) is becoming increasingly popular, especially in areas prone to experience drought. Water can be pumped into an aquifer through injection wells or spread across acres of land allowing the water to percolate into the aquifer. This type of water storage is often done using surface supplies when water is plentiful. Instead of allowing the surface water to flow to the ocean, it can be diverted into an underground storage “bank”.

    What is Water?

    When discussing water, sometimes we often overlook the very unique qualities of this vital resource. Water is composed of three (3) atoms. There are two (2) hydrogen atoms attached to one (1) oxygen atom. The bonding of these atoms to form a water molecule is what truly gives water its amazing characteristics. A water molecule is a polar compound, meaning it has the hydrogen ion bonds angled away from the oxygen atom. The oxygen atom has an affinity for positively charged ions while the hydrogen atoms attract negatively charged ions. This polarity allows water to bond with a variety of compounds making water a “universal” solvent. Water is found in three different phases; liquid, solid, and gas.

    C:\Users\johnson_a\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.Outlook\MUCOC6NG\Water 020 Page 71 H2O.jpg
    Figure \(\PageIndex{1}\): –Water molecule.

    The ability of water to attract other water molecules is called cohesion. This characteristic creates surface tension of water. A simple experiment to see surface tension in action is to float a paper clip on water. Fill a glass and gently place a paper clip on the water. The surface tension among the water molecule bonds allows the paper clip to float. Adhesion is ability of water to attract other molecules. This attraction to other molecules can be seen by the meniscus in a cylinder. Water attaches to the sides of the cylinder causing it to “creep” up the sides. Some substances are not attracted to water molecules preventing them from dissolving in water. For instance, fats and oils are considered hydrophobic because they do not dissolve in water. Conversely, hydrophilic substances such as salts and sugars dissolve quite easily in water.

    Water Rights

    Does everyone have a right to water? Well, on the surface this seems like an easy answer. Everyone should have the right to a safe, clean, and affordable water. However, this isn’t always the case. Water rights laws are very complex and simply stating everyone has the right to access drinking isn’t always enough. Typically, in highly populated cities, the “right” to water isn’t a big issue. However, accessing a safe, clean, and reliable supply in rural areas isn’t always possible, let alone feasible. In 2012, California enacted Assembly Bill 685 establishing a state policy that every Californian has a human right to safe, clean, affordable, and accessible drinking water. This sounds great, but making this a reality is very difficult to accomplish, especially in very rural areas where the infrastructure doesn’t exist to provide the water. Who actually “owns” the water we use every day?

    Water rights are held by a variety of different private and public entities. Individual farmers can own water rights as well as large municipalities. Water rights are commonly land-based rights. Rights can be allocated based on land ownership or possession. Another type of water right is termed “riparian” rights. This type of land-based right gives the owner of land adjacent to the bank of a water body the right to the water flowing next to their property. Water rights can be also based on use. Use-based rights grant the user certain rights based on the amount of water previously used. Use is given for certain beneficial uses. This can also be for municipalities serving a certain population. Most water rights are associated with surface water supplies. Groundwater is often left to the people owning groundwater wells and pumping water out of the underlying aquifer system. At times this can be contentious if one entity is considered to be pumping more water than others deem is appropriate for the area and or use. This type of contention can result in something called adjudication. Adjudication is a legal process to determine who has a valid right to the water and how much of it can be used by each entity.

    This page titled 1.8: Water Supply is shared under a CC BY license and was authored, remixed, and/or curated by College of the Canyons (ZTC Textbooks) .