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Water Currents: Tapped Out: How Will Cities Secure Their Water Future?


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Water depletion tapped out map

Half of all cities with populations >100,000 are located in water basins in which more than half of available water supplies are being depleted during some portion of the year.

Today, global demands for food, energy, and shelter are putting unprecedented pressure on the resources of the planet. Water is at the heart of this crisis.

In fact, more than half of the world’s cities are already experiencing water shortages on a recurring basis – based on findings from a study that I published, along with 13 of my colleagues, this week in the Water Policy journal. These water-stressed cities are finding it extremely difficult and expensive to secure the additional water supplies needed to support their growth.

Our study, “Tapped Out: How Can Cities Secure Their Water Future?” highlights the reality that many growing cities are badly in need of new, low-cost, and reliable sources of water. We found that a key strategy cities should consider is to form partnerships with agricultural producers to conserve water use on farms, thereby freeing up water that can be used in the city.

Even a modest level of reduction (15-20 percent) in agricultural water consumption, globally, could make more water available than all the water consumed in cities and industries today.

Where Did all the Water Go?

In conducting the study, we identified cities around the world that are situated in water-scarce regions, and then assessed how water is being used in those regions.

It was not difficult to see why so many cities got into trouble with water.

The water sources they depend upon – rivers, lakes, and aquifers – have for decades been heavily used for irrigated agriculture.  Since 1950, the consumption of water globally for irrigation has tripled in volume, a trend that played a large role in enabling food production to more than double over the same period.

The result:  Water-stressed cities are trying to expand in places where most of the water is already being consumed by irrigated agriculture. In fact, more than 90% of the water being consumed from those shared water sources is going to growing crops.

In particular, we closely examined the challenges and responses of four cities: Adelaide, located just outside but dependent upon the Murray–Darling River Basin of Australia; and three cities in the U.S.: Phoenix, located in the Gila River Basin in Arizona; San Antonio, dependent on the Edwards Aquifer in Texas; and San Diego, which relies upon the San Diego, Colorado, and Sacramento River Basins in California.

The Unsustainable Pursuit of More Water

Looking at the investments that these cities have made – and plan to make in the future – to access more water, we found similar patterns in their water development: 1) They began by exhausting their local surface and groundwater supplies; then 2) imported water from other rivers and aquifers; and finally 3) turned to recycling of wastewater or stormwater, or desalination of either seawater or brackish groundwater.  We found that water conservation efforts did help mitigate, to varying degrees, the timing of water-system expansions and the extent to which cities had to rely on new sources of supply.

Fig. 10 - Phoenix Supply Color - no title

Trends in water supply sources for the Phoenix metro area.

We found this typical water development pattern to pose significant problems from a sustainability perspective – as it is usually associated with serious negative ecological and social impacts – and lacking cost effectiveness.

The heavy exploitation of freshwater sources – a result of growing urban demands on top of heavy agricultural use – has caused severe damage to freshwater ecosystems, impaired the ability of ecosystems to provide services to people, and created health problems in many regions. In addition, groundwater depletion (lowering of underground water levels) has led to increased electricity costs for pumping the water from ever-increasing depths.  When cities extend their reach into other rivers or aquifers to access water supplies, they spread negative impacts over great distances. Energy-intensive technologies such as recycling and desalination are expensive, resulting in higher water bills for consumers as well as increased carbon emissions that accelerate climate change.

Fig. 9 - Colorado River Decline - no title

Water flows in the lower Colorado River have been heavily depleted by agricultural irrigation and urban water consumption, resulting in considerable damage to the river ecosystem and its species. This has in turn led to severe impacts on indigenous cultures dependent on fish and other resources in the delta.

So, what can be done?

Place Your Bets on Water Conservation

Far and away, water conservation is the most cost-effective, immediate, and environmentally desirable means for addressing water shortages.  But few cities have maximized their conservation potential.

Fig. 18 - San Diego Future Costs - no title

This comparison of the costs of future water supply options for San Diego illustrates the impressive cost-effectiveness of both urban and agricultural water conservation.

In addition to investing in urban water conservation – e.g., by installing low-water plumbing fixtures, fixing leaks in water distribution lines, or reducing landscape watering – considerable potential exists to make more water available locally by reducing water consumption in irrigated agriculture.

Promising opportunities exist to free up the water presently used in agriculture through techniques such as reducing unproductive water consumption (e.g., stopping canal leakage, reducing soil and reservoir evaporation), changing crop types, introducing rotational fallowing, temporary fallowing during droughts, or the elimination of low-value farming.

In our recommendations for water sharing going forward, we advocate for ‘urban–rural partnerships.’ While there are formidable hurdles to forming urban–rural partnerships to share water (these challenges are detailed in our paper), the payoff is too big to ignore.

In many basins, a reduction of agricultural water consumption of just 10–20% can yield massive volumes of water that can be saved for other uses. For example, if adopted globally, this level of reduction in agricultural water consumption would make more water available than all the water consumed in cities and industries today.

A Role for Markets?

Our paper also highlights the role of water markets in facilitating water sharing and transfers of water rights among cities, farmers, and environmental interests.  For example, my organization, The Nature Conservancy, is exploring how to expand water markets more broadly. In places where water markets exist, such as the Murray-Darling Basin in Australia or in the Edwards Aquifer of Texas, we see the potential for multi-win benefits to farmers, cities, and the environment. Just as a farmer can sell “saved” water to other farmers, or cities, we can serve as the buyer or help facilitate the purchasing of a water right, and allow the water to remain in the river or aquifer to support ecological health and water availability for other uses.

In addition to the Murray-Darling and Edwards Aquifer, we are looking at opportunities to buy water for conservation purposes in the Guadalupe River in Texas, the Colorado River Delta, and other places.  We are also working with local governments and water users in the U.S. and abroad to create new water markets, or to improve the functioning of existing markets, so that water is available to those that need it most.

But perhaps most important of all, we are also working with governments to help them understand the hazards of overusing a water source.  When too much water is being taken from a river, lake or aquifer, everyone is at risk!


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