That’s the conclusion from a new study in the journalWater Policy, whose authors compared the water supplyhistories of four cities — San Diego, Phoenix, SanAntonio, and Adelaide, Australia. Among the lessonslearned? Urban water conservation, recycling, anddesalination aren’t silver bullets. In fact, the best solutionmay lie upstream with farmers — saving just 5-10 percentof agricultural irrigation in upstream watersheds couldsatisfy a city’s entire water needs.But the time to act is now, argues Brian Richter, a seniorfreshwater scientist at The Nature Conservancy and thestudy’s lead author — he says a global urban water crisis isalready here. Below, Richter tells us more about what citiesneed to do to say on the right side of dry.
Q. Many cities take a similar pattern of waterdevelopment, according to your research – going fromexhausting local surface and groundwater supplies toimporting water to implementing water conservation tofinally recycling water or desalination. Why is this patternunsustainable?A. When we overuse a freshwater source, we set ourselvesup for disaster. Each of the cities we reviewed in our studyhas contributed to the drying of a major river or importantgroundwater spring. That has obvious ecological impactsand social consequences — it affects livelihoods andhuman health by compromising fishproduction, concentrating pollution, or curtailingrecreational activities.
Our research is revealing that water scarcity also causessevere economic losses by limiting or disruptingagricultural, industrial, and energy production. Texas lostnearly $8 billion in agriculture last year due to watershortages; electricity generation from hydropower dams onthe Colorado River in 2010 dropped by 20 percent due towater shortages. Some estimates suggest that China maybe losing $39 billion each year due to crop damage andlessened industrial production, and hundreds of thousandsof people around the globe are being forced to move dueto water shortages.Because these impacts are so pervasive and damaging, weneed to begin investing in water supply approaches thatdon’t just minimize these adverse impacts but insteadbegin to reverse them.
Q. Are we looking at a crisis in securing urban watersupplies in the near future, either for U.S. cities orglobally?A. That crisis is already upon us. Our study revealed thathalf of all cities — both in the United States and globally —are located in watersheds where more than 50 percent ofthe renewable supply of water to our rivers and aquifers isbeing consumed, at least seasonally. Now, that’s not aproblem 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’tenough water to meet all needs.
Q. Phoenix, another one of your case studies, has lowered its percapita water use by 25 percent since 1990 through various waterconservation measures — and yet Phoenix is water scarce. Why?A. Water scarcity results when we heavily deplete a freshwatersource. It doesn’t necessarily mean that you’re experiencingregular water shortages in your home or business. But it doesmean that you’re at considerable risk if the water suppliescontinue to be increasingly depleted by other users, or you getinto a drought situation.Phoenix’s water conservation efforts are admirable, but they needto do much more. They are heavily dependent on the ColoradoRiver, which is so thoroughly overused that it dries up beforereaching its delta in the Gulf of California. During asevere, prolonged drought, the reliability of that water source willbe in jeopardy.
Q. So storm- and wastewater recycling aren’t enough?A. Contrary to popular belief, water conservation and recyclingmay not result in a net improvement in the affected water source.If the water that’s conserved is simply used to supply additionalurban growth, then the water source is no better off.The vast majority (80-90 percent) of water used in cities isreturned to the freshwater source after use. So only 10-20percent of the water is ―lost‖ or ―depleted‖ — most of that goesto outdoor landscaping or golf courses. Water recycling shuts offthe return of water to the freshwater source — instead ofdischarging the used water back to a river, the water is used fordomestic, commercial, industrial, or agricultural purposes.So water recycling will ―save‖ water — and reduce water scarcityin the freshwater source — only if it reduces the fraction of waterthat was previously being lost from the freshwater system.
Q. What about desalination if you’re a city on the coast? It’sexpensive — but Adelaide’s desal plant is supposed to providemore than 25 percent of that city’s water supply by 2013.A. Desalination could be a wonderful solution to our waterchallenges — more than one in every two people on Earth livesnear a coast. But removing salts from ocean water requires atremendous amount of energy, and the expense of that energymakes desalination the most costly way by far to supply freshwater to cities.And there’s a wicked climate change feedback loop fordesalination: using it to create fresh water produces carbonemissions that change our climate, which in turn affects theprecipitation that supplies fresh water. Without a radicalbreakthrough in energy production, desalination will continue tosupply only a tiny fraction of the world’s freshwater needs. (Notethat Adelaide is using 100 percent renewable energy to power itsdesalination plant.)