Bad news about the water supply keeps rolling in. In July, a study on the groundwater in the Colorado Basin found that 53 million acre-feet of water (65 billion cubic meters) had been depleted between December 2004 and November 2013. The historic drought in the western United States is so severe that it is causing mountains to rise. And ominous signs of water scarcity are not limited to the United States. Farmers in Vietnam are converting rice paddies to shrimp farms as the dry season gets dryer and the rising South China Sea turns coastal freshwater ponds salty. Water scarcity threatens much of the world economy, from the food industry to the mining industry to the petrochemical industry.
Though climate change accounts for a part of the unfolding water crisis, water management practices are driving the problem. Water has long been treated as a free and inexhaustible raw material. As a result, it’s used inefficiently. While great progress has been made in increasing awareness of energy efficiency, water continues to be taken for granted. Without major changes, two-thirds of the world’s population could be living in water-stressed conditions by 2025.
Water Scarcity and the Built Environment
Buildings account for about 12% of water use in the United States. Already, water conservation efforts and greater efficiencies in using water have led to a reduction in water withdrawals. But, for further gains, fundamentally rethinking the built environment is necessary. For the most part, everything that needs water in a building is provided with potable freshwater. Similarly, all wastewater is treated the same. But not everything needs potable water. And rather than being disposed of, some wastewater can be recycled. Water from a sink can be reused to flush a toilet. Water from a bathtub can be used for landscape irrigation. When water is cheap and abundant, it makes sense to have a single system for all water needs and a single system to dispose of all “used” water. But meeting all water needs with potable water may soon no longer be an option.
Similar recycling efforts can be achieved with stormwater runoff. Many municipalities treat stormwater runoff and domestic sewage the same, using a combined sewer system to transport them in a single pipe to a sewage treatment plant (though heavy rainfall or snowmelt can create undesirable outcomes for combined sewers). Rather than building infrastructure to capture and transport stormwater through gutters and sewers, capturing it to recharge groundwater or for direct nonpotable consumption can directly improve the water situation. Indeed, the Pacific Institute estimates that urbanized Southern California and the San Francisco Bay region have the potential to increase water supplies by 420,000 to 630,000 acre-feet per year simply by better managing stormwater runoff.
One Word: Graphene
Of course, when we talk about water scarcity, we refer to only freshwater, which accounts for only 2.5% of total global water. Desalinating abundant seawater is a seemingly attractive workaround, a way to solve water scarcity without the difficult task of changing water use habits. Unfortunately, desalination, for now, is expensive and energy-intensive. The most common form of desalination, reverse osmosis, forces seawater through a polymer membrane. The membrane allows water molecules to pass, but blocks salt molecules.
Graphene, an allotrope (i.e., a different structural form) of carbon, which shows promise in battery technology, quantum computing, health monitoring, and solar cells, could reduce the cost and energy associated with desalinating water. The gaps in polymer membranes are determined by the physical and chemical properties of the polymer used. Gaps in graphene must be punched, so they can be sized to reduce the amount of pressure needed to pass water through but still prevent salt from passing through. Lockheed Martin and the Massachusetts Institute of Technology are both working on overcoming the engineering problems associated with graphene membranes. Commercial viability may still be several years away, but graphene may make desalination accessible enough to meet the world’s needs for clean water.