Living Within Nature’s Water Limits

The map above indicates regions of the world that are reaching the limits of their renewable water supply. Yellow areas indicate places where more water is being consumed than is being replenished during droughts. Orange areas reach the sustainable limit during certain seasons each year. Red zones are exhausting their renewable supplies chronically. Map adapted from Brauman et al 2016, “Water depletion: An improved metric for incorporating seasonal and dry-year water scarcity into water risk assessments.”

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At least 30% of global water consumed today is being supplied from over-exploited, non-sustainable water sources, meaning our water extractions are exceeding ecologically safe or sustainable levels. This percentage is projected to increase to 50% in coming decades with climate change if concerted, effective actions are not implemented.

This is not good. In fact, it’s downright frightening. In the colored areas of the map above, farmers are running out of irrigation water. Power plants are shutting down for lack of cooling water. Even cities are turning off taps in homes and businesses. You can find many of these stories in this interactive map.

The good news is that proven strategies exist for bending the arc toward a more water-secure future. In my Chasing Water book I described many of them. In the book I highlight what I consider to be the single most powerful first step for getting water scarcity under control. It’s called a ‘water cap.’

When imposed on any particular water source, such as a river, lake, or aquifer, a cap prevents water use from exceeding a predetermined limit. Such a cap may take the form of monthly or annual volumetric limits on water consumption. Alternatively, a limit can be set as a water level that should never be exceeded, such as the minimum level of groundwater in an aquifer, or the level of a lake’s surface. Capping can also begin by instating a moratorium on new wells or diversions, thereby preventing the overuse of water from worsening. When applied properly, a cap prevents extractions from exceeding the rate at which a water source is being replenished, and it also protects adequate river flows and wetland or lake levels to sustain healthy freshwater ecosystems.

While I was personally aware of many successful examples of cap-setting from my work projects around the globe, I’d never had the chance to carefully and systematically evaluate their performance on a broad scale. Last year, I recruited 19 bright and energetic students at the University of Virginia to scrutinize case studies of water caps from around the world. They compiled a database of 47 examples from 14 countries.

With Charles Wight of Oxford University and now at Water Witness International, we evaluated each capping case study on the basis of adaptability, enforcement, and performance of the cap. In our paper published last week in the Water Policy journal, we found that more than 40% of the cases appeared to be performing as intended, i.e., the caps were clearly working. Just as importantly, it wasn’t hard to discern why the cases not yet performing well were struggling.

47 case studies of water caps were evaluated and ranked across three categories. 1 is low score, 3 is high score.

For example, in many cases the cap was not sufficiently and clearly quantified to enable effective enforcement. Sometimes the cap was not set at a level sufficient to stop the water source from being further depleted. In some regions, water use is not authorized using permits or water rights, making it difficult or impossible for water managers to enforce a cap. Many places don’t have sufficient management capacity to monitor the condition of the water source or the use of its water. Also interesting was the fact that the most successful caps were set through an inclusive, transparent process involving the water users that would be affected by the cap.

The most important influence of a water cap is that it sends a powerful message that we can’t continue to use more water than is being replenished; we can’t continue to live beyond nature’s water limits. When that message is heard and understood, water users respond by innovating and getting creative with their water use so that they’re able to thrive with less water. In many instances, the initiation of a water cap stimulates a water conservation economy, in which technologies and expertise advance rapidly. It creates water-conserving cultures and communities.

We hope that our research and case study summaries will be useful to water managers and communities struggling with water scarcity. There are many valuable lessons to be learned, and we hope that our paper can help illuminate some pathways to water security.