In January, Brian Richter, director of freshwater strategies at The Nature Conservancy, spelled out four water resolutions through a thought-provoking series of blog posts. One of those resolutions was to better understand and communicate the differences between water use and water consumption. This is a particularly important issue, as there has been a lot of discussion lately about water scarcity, water stress, and the risks associated with them.
So what do ”water use” and “water consumption” mean?
- “Water use”describes the total amount of water withdrawn from its source to be used. Measures of water usage help evaluate the level of demand from industrial, agricultural, and domestic users. For example, a manufacturing plant might require 10,000 gallons of freshwater a day for cooling, running, or cleaning its equipment. Even if the plant returns 95 percent of that water to the watershed, the plant needs all 10,000 gallons to operate.
- “Water consumption”is the portion of water use that is not returned to the original water source after being withdrawn. Consumption occurs when water is lost into the atmosphere through evaporation or incorporated into a product or plant (such as a corn stalk) and is no longer available for reuse. Water consumption is particularly relevant when analyzing water scarcity and the impact of human activities on water availability. For example, irrigated agriculture accounts for 70 percent of water use worldwide and almost 50 percent of that is lost, either evaporated into the atmosphere or transpired through plant leaves.
Water Consumption and Use Both Need to Be Measured
Understanding both water use and consumption is critical to evaluating water stress. Measures of water usage indicate the level of competition and dependency on water resources. For example, domestic water use per capita in Qataris one of the highest in the world, due in part to the free supply of water to Qatari nationals and limited rainfall. Although most of that use is non-consumptive, in an emergency, the country would only have enough water for 48 hours. Additionally, water is rarely returned to a watershed in perfect condition after being used by industry, agriculture, and other users, and change in quality contributes to water stress levels. Water consumption estimates, on the other hand, help gauge the impact of water use on downstream water availability and are essential to evaluating water shortages and scarcity at the watershed level, including impacts to aquatic ecosystems.
Therefore, a holistic understanding of water stress requires analysis of both the total use and consumption of water.
A Holistic Understanding of Water Stress
WRI’s Aqueduct Water Risk Atlas accounts for the impact of both water use and consumption by using a baseline water stress indicator. Baseline water stress measures total annual water use from municipal, industrial, and agricultural sectors expressed as a percent of the total annual available water after all upstream water consumption has been subtracted. By acknowledging both total water usage and consumption, Aqueduct users can rely on the baseline water stress indicator to evaluate overall freshwater demand and availability in specific watersheds.
Already, more than 1.4 billion people live in river basins where the use of water exceeds the minimum recharge levels. In the next 12 years, water withdrawals in developing countries are predicted to increase by 50 percent. Measuring water usageand consumption is critically important for identifying areas that are at risk of water scarcity and excessive competition amongst users. After all, in order to prevent or manage water risk, we must first fully understand it.