1.2: Sources and Characteristics of Water
This chapter will discuss the sources of water in California and the characteristics of water.
Student Learning Outcomes
After reading this chapter, you should be able to:
- Explain the different stages of the hydrologic cycle
- Identify the various sources of supply
- List the primary sources of supply for the Southern California area
- Discuss the physical, chemical, and biological aspects of water
Hydrologic Water Cycle
Where does our water come from? One of the most unique aspects of our planet is the vast amount of water covering it. About seventy-one (71) percent of the earth’s surface is water. The very thing that is essential to sustain life covers almost three-quarters of our planet. However, approximately ninety-seven and a half (97.5) percent of all the water on earth is saltwater. This equates to about three hundred twenty-six (326) million trillion gallons of water, which is not suitable for drinking. This means two and a half (2.5) percent of the planet’s water is freshwater, or water not containing salt. While this is still a lot of water, almost seventy (70) percent of it is inaccessible. This water is in the form of glaciers or permanent snow cover. Approximately thirty-one (31) percent of this water is groundwater and less than one (1) percent is considered surface water.
Does this mean we will eventually run out of freshwater? If the majority of the earth’s water is either saltwater or inaccessible, does it mean we have a limited supply to sustain life? The short answer is no, we will not run out of freshwater and we do not have a limited supply. However, access to freshwater is an issue that needs to be addressed, and there are places on our planet that lack safe and adequate supplies of drinking water. In this section, we will address the “short answer”. The reason we have access to freshwater in most areas on earth has to do with something known as the hydrologic cycle. The hydrologic cycle is the continuous movement of water throughout the earth. It is the physical process of evaporation, condensation, precipitation, infiltration, and surface runoff. Water changes from one form to another and then another. The three phases that water passes through are liquid, gas, and solid. We understand and encounter water in these three phases on a daily basis. Water in its most common form is liquid. However, we can freeze it to make ice (solid) or boil it to encounter steam (gas). Throughout the hydrologic cycle, water also transfers through these phases.
The image below (courtesy of the United States Geological Survey - USGS) shows a lot of detail regarding the hydrologic cycle. First, try to focus on the three phases we just discussed (liquid, gas, and solid). Precipitation is the liquid state, ice and snow the solid state, and evaporation represents the gas or vapor state. As you can see from this diagram, it is a little more complicated, but water passes through these three phases (states) in a continuous movement on, above, and below the surface of the earth. There are three (3) other terms you should become familiar with in this process. The terms are evapotranspiration, infiltration, and sublimation.
Evapotranspiration is the process of water transferring from the land to the atmosphere from the soil and other surfaces and by transpiration from plants. Transpiration is the evaporation from plant leaves. Think of it as plants sweating. Sublimation is the process by which a substance (water in this case) passes directly from the solid phase to the vapor or gaseous phase. This typically happens in the atmosphere. The third term is infiltration. Infiltration is the process of water entering the ground surface. If geological conditions are right, the water will continue transferring deeper into the earth’s surface until it becomes groundwater. This deeper transferring process is known as percolation. The only other process in the hydrological cycle you should take note of is the process of condensation. This is when water vapors transition from the gas phase to the liquid phase. Now that we have a general understanding of the hydrologic cycle, it’s time to turn our attention to the various sources of water supply.
Water Sources
Surface Water
As water leaves the oceans and other areas on land, it evaporates into the atmosphere and eventually comes back down through some form of precipitation. As snow and ice melt or rain falls on land it becomes runoff. This runoff will enter streams, rivers, or lakes. These are considered surface water. There are three (3) main surface water sources of supply in southern California, State Water Project, Colorado River Aqueduct, and Los Angeles Aqueduct. Each of these surface water sources serve specific areas and are owned and operated by different water agencies.
- Los Angeles Aqueduct – The LA Aqueduct is owned and operated by Los Angeles Department of Water and Power (LADWP). The only users of this water are the customers of LADWP. The aqueduct took approximately five (5) years to construct and originates in the Owen’s Valley, bringing water to LADWP customers through an all gravity system.
- Colorado River Aqueduct – The Colorado River Aqueduct brings water from the Colorado River at Lake Havasu to Southern California. It is operated by Metropolitan Water District. The water flows through two (2) reservoirs and five (5) pumping stations and delivers water as far south as San Diego County.
- State Water Project – The State Water Project is one of the largest public water utilities in the world. It brings water from Northern California and distributes it to areas in and around San Francisco and to the major metropolitan areas of Southern California. It is maintained by the California Department of Water Resources and has twenty-nine different contractors pulling water from this system. There are more than a dozen water storage reservoirs and pumping plants within this system.
According to the USGS, approximately eighty (80) percent of all water used in the United States comes from surface water sources. Surface water is an important natural resource used for many purposes, especially irrigation and public drinking water supply.
Groundwater
Groundwater is water on the surface, which infiltrates and eventually percolates deep enough into underground systems known as aquifers. An aquifer is an underground system of permeable soil (sand, gravel, rock), which can contain and transmit water underground or groundwater. Groundwater exists for two main reasons, gravity and geologic formation.
Gravity pulls the water into the earth and if the geologic formation is conducive to holding water, aquifers will form. Water accumulates in the voids and spaces within the underground geology. Some examples of these formations consist of sandstone, limestone, and even granite. There are three (3) main types of aquifers, unconfined, confined, and fractured rock. Each of these has unique characteristics and properties.
- Unconfined Aquifer – An unconfined aquifer has the upper surface open to the atmosphere through permeable material such as sand and gravel. This type of aquifer is typically more susceptible to contamination from spills or discharges on the ground surface.
- Confined Aquifer – A confined aquifer has a similar composition as unconfined aquifers. They consist of porous materials such as sand and gravel. The main distinction is there is an overlying impervious rock or clay layer separating it from the atmosphere. Commonly, this impervious layer consists of clays. Because of this impervious layer, confined aquifers are generally less susceptible to contamination.
- Fractured Rock – An underground fractured rock aquifer system is much different than unconfined and confined aquifers. In some areas, there are rock formations, which have little to no permeability, but they still can contain water. The water is stored in complex fractures (cracks) within the rock formation. This water can be withdrawn, but the variability of the fractures makes it more difficult to locate the areas with water.
Both unconfined and confined aquifers can yield large quantities of water for domestic and agricultural use. Many communities rely solely on groundwater from these types of aquifers. While fractured rock can store water underground, these types of aquifer are not as common and do not produce nearly as much water. In the Southern California area, there are many different aquifers systems. According to the California Department of Water Resources (DWR), there are seventy-seven (77) groundwater basins and subbasins in the South Coast Hydrologic Region. This includes the counties of Ventura, Los Angeles, San Bernardino, Riverside, Orange, and San Diego.
Recycled Water
Another source of supply, which is becoming more prominent and needed is recycled water. In the past, the term “reclaimed” water was used more frequently. This was due in part to the source of the water, water reclamation plants. However, as the use became more prevalent, the term recycled became more common. They are interchangeable.
Recycled water is treated wastewater. All wastewater travels through a network system of sewer pipelines. This network is primarily a gravity flow system, but at times when elevations change, pumps are required to “lift” the wastewater. Once the wastewater arrives at a wastewater reclamation plant (wastewater treatment plant is also commonly used), it must go through a treatment process. The treatment requirements for ultimate discharge vary depending on where the treated wastewater will be released. Sometimes these treatment plants are located along the coast and the water is discharged to the ocean. While other times, plants are located in inland communities and the water is discharged in local river systems.
In order for treated wastewater to be used as recycled water, it must at least go through tertiary treatment. The first two stages of wastewater treatment (primary and secondary) are designed to remove the debris and solids through a sedimentation process and then a process to remove the biological content. The tertiary treatment process is usually the last stage of treatment unless some form of advanced treatment is used. Typically this process involves some form of filtration, which includes sand. Additional nutrients can also be removed.
While recycled water typically meets all state and federal drinking water standards, it is not allowed for human consumption. The primary use of recycled water is irrigation. Parks, playgrounds, sports fields, street and freeway landscaping, and golf courses are some of the more common uses of recycled water. Recycled water can also be used for industrial and commercial cooling systems.
Water Characteristics
Water is an amazing compound and has some very unique properties. Because of the molecular structure of water, it has an affinity for other molecules. Water is considered a “polar” compound. This means there is an uneven distribution of the electron density. The bonds between the oxygen atom and two hydrogen atoms are at an angle (see below).
The red dot above represents the oxygen atom in water and the two white dots represent the hydrogen atoms, which equates to the molecular formula “H2O”. The structure of water has a partial negative charge near the oxygen and partial positive charge near the hydrogen atoms. This structure allows water to have both cohesion and adhesion properties. Cohesion is the ability of water to be attracted to other water molecules. This cohesive property is what gives water surface tension and allows insects such as a Water Strider to walk on water. This polarity also allows water to dissolve many different compounds.
Water also has an attraction between molecules. This property is referred to as adhesion. When you fill a glass with water the water around the glass “adheres” to the glass causing the water to “climb” the glass wall. This results in the water having a meniscus a concave appearance.
Water is also the only common substance on the earth’s surface, which exists as a gas, liquid, and solid. Temperature effects water by causing it to persist in each one of these phases. It is typically a colorless and odorless substance.
Physical Characteristics
Water is generally colorless. This is one of the most important aesthetic qualities of water, which customers care about. No one wants to drink water that has a color. However, this is also a common problem water quality professionals have to monitor. There are several things in the distribution system, which can cause water to have a color. Some examples include air (white), iron (yellow or brown), manganese (causing black stains). There are solutions to these examples, but it is important for water utility professionals to monitor their water quality within the distribution system in order to keep water in its natural colorless state.
In addition to being colorless, water typically doesn’t have a taste. However, much like color, certain things in the water supply can give water an unpleasant taste. Chlorine is a chemical commonly used to disinfect water in order to make it safe to drink. However, this can also give water an unpleasant taste to customers.
The final physical property of water we will discuss in this text is temperature. As the temperature of water changes, the physical nature of water also changes. For example, as water approaches 0°C it changes form from a liquid to a solid. Conversely, as water approaches 100°C, it starts to boil and transitions from a liquid to a gas.
Sample Questions
-
Which one is not one of the phases of water throughout the hydrologic cycle?
- Liquid
- Gas
- Solid
- Sublimation
-
Treated wastewater used for irrigation is termed ___________.
- Non-potable water
- Irrigated supply water
- Agriculture water
- Recycled water
-
Water is generally ___________.
- Colorless
- Unsafe to drink
- Abundant in all areas
- All of the above
-
Which of the following would not be considered an aquifer?
- Confined
- Unconfined
- Aqueduct
- Fractured rock
-
The three main surface water sources of Los Angeles include all of the following except ___________.
- Los Angeles Aqueduct
- Columbia River
- Colorado River
- State Water Project