Groundwater is also an important source of water in California. In a normal year about
40% of the state’s water supply comes from groundwater. In a drought year, the number
can rise to 60% or more. The largest groundwater reservoirs are found in the Central Valley
where thousands of years of snow melt has fed the aquifers. In many locations, much more
groundwater is used each year than is available to recharge the aquifer. Subsidence of the
land is common in these regions.
Despite these vast water sources, the states large population and enormous agricultural
landscape put a strain on the water supply. Water rights in California are complex and
controversial. Although about 75% of the water resources are in the northern one-third of
the state, the largest usage, about 80%, is in the southern two-thirds. Besides projects that
exist to distribute water within the state, a large source of water is the Colorado River, which
California must share with five other states and Mexico. The distribution of water resources
in the Western United States will be a topic of much discussion in the coming decades.
Lesson Summary
- Human water use can be lumped into five categories. The uses are arranged in order
of greatest to the least amounts of total water use on Earth: - Agriculture (sixty-nine percent)
- Industry uses (fifteen percent of global water use)
- Home and Personal use (fifteen percent)
- Recreation uses (less than one percent)
- Environmental use (less than one percent)
- Despite California’s abundant water supply from surface streams and groundwater, the
state has a number of water rights issues that will be important long into the future.
Review Questions
- Describe the three water uses that consume the most fresh water.
- Explain why humans are limited to using less than one percent of all the water on
Earth for our needs. - List two reasons why human water use has increased tremendously during the past
century. - Describe four consequences of water shortages.
- What does the phrase ’water is more valuable than gold’ mean?
- Describe why some water uses are called consumptive.
- Describe drip irrigation and why it wastes less water than irrigating with sprinklers.
- Describe why droughts are more serious in arid regions of the world than in wetter
regions.