2. That’s the conclusion from a new study in the journal
Water Policy, whose authors compared the water supply
histories of four cities — San Diego, Phoenix, San
Antonio, and Adelaide, Australia. Among the lessons
learned? Urban water conservation, recycling, and
desalination aren’t silver bullets. In fact, the best solution
may lie upstream with farmers — saving just 5-10 percent
of agricultural irrigation in upstream watersheds could
satisfy a city’s entire water needs.
But the time to act is now, argues Brian Richter, a senior
freshwater scientist at The Nature Conservancy and the
study’s lead author — he says a global urban water crisis is
already here. Below, Richter tells us more about what cities
need to do to say on the right side of dry.
3. Q. Many cities take a similar pattern of water
development, according to your research – going from
exhausting local surface and groundwater supplies to
importing water to implementing water conservation to
finally recycling water or desalination. Why is this pattern
unsustainable?
A. When we overuse a freshwater source, we set ourselves
up for disaster. Each of the cities we reviewed in our study
has contributed to the drying of a major river or important
groundwater spring. That has obvious ecological impacts
and social consequences — it affects livelihoods and
human health by compromising fish
production, concentrating pollution, or curtailing
recreational activities.
4. Our research is revealing that water scarcity also causes
severe economic losses by limiting or disrupting
agricultural, industrial, and energy production. Texas lost
nearly $8 billion in agriculture last year due to water
shortages; electricity generation from hydropower dams on
the Colorado River in 2010 dropped by 20 percent due to
water shortages. Some estimates suggest that China may
be losing $39 billion each year due to crop damage and
lessened industrial production, and hundreds of thousands
of people around the globe are being forced to move due
to water shortages.
Because these impacts are so pervasive and damaging, we
need to begin investing in water supply approaches that
don’t just minimize these adverse impacts but instead
begin to reverse them.
5. Q. Are we looking at a crisis in securing urban water
supplies in the near future, either for U.S. cities or
globally?
A. That crisis is already upon us. Our study revealed that
half of all cities — both in the United States and globally —
are located in watersheds where more than 50 percent of
the renewable supply of water to our rivers and aquifers is
being consumed, at least seasonally. Now, that’s not a
problem as long as we’re receiving plentiful precipitation.
But if you’re using that much water on an average,
ongoing basis and you go into a severe drought, there isn’t
enough water to meet all needs.
6. Q. Phoenix, another one of your case studies, has lowered its per
capita water use by 25 percent since 1990 through various water
conservation measures — and yet Phoenix is water scarce. Why?
A. Water scarcity results when we heavily deplete a freshwater
source. It doesn’t necessarily mean that you’re experiencing
regular water shortages in your home or business. But it does
mean that you’re at considerable risk if the water supplies
continue to be increasingly depleted by other users, or you get
into a drought situation.
Phoenix’s water conservation efforts are admirable, but they need
to do much more. They are heavily dependent on the Colorado
River, which is so thoroughly overused that it dries up before
reaching its delta in the Gulf of California. During a
severe, prolonged drought, the reliability of that water source will
be in jeopardy.
7. Q. So storm- and wastewater recycling aren’t enough?
A. Contrary to popular belief, water conservation and recycling
may not result in a net improvement in the affected water source.
If the water that’s conserved is simply used to supply additional
urban growth, then the water source is no better off.
The vast majority (80-90 percent) of water used in cities is
returned to the freshwater source after use. So only 10-20
percent of the water is ―lost‖ or ―depleted‖ — most of that goes
to outdoor landscaping or golf courses. Water recycling shuts off
the return of water to the freshwater source — instead of
discharging the used water back to a river, the water is used for
domestic, commercial, industrial, or agricultural purposes.
So water recycling will ―save‖ water — and reduce water scarcity
in the freshwater source — only if it reduces the fraction of water
that was previously being lost from the freshwater system.
8. Q. What about desalination if you’re a city on the coast? It’s
expensive — but Adelaide’s desal plant is supposed to provide
more than 25 percent of that city’s water supply by 2013.
A. Desalination could be a wonderful solution to our water
challenges — more than one in every two people on Earth lives
near a coast. But removing salts from ocean water requires a
tremendous amount of energy, and the expense of that energy
makes desalination the most costly way by far to supply fresh
water to cities.
And there’s a wicked climate change feedback loop for
desalination: using it to create fresh water produces carbon
emissions that change our climate, which in turn affects the
precipitation that supplies fresh water. Without a radical
breakthrough in energy production, desalination will continue to
supply only a tiny fraction of the world’s freshwater needs. (Note
that Adelaide is using 100 percent renewable energy to power its
desalination plant.)
