Climate change impacts access to water, but a new study suggests that big cities eager to avoid future water crises might want to measure how much wealthy residents are using to fill their swimming pools, irrigate their lawns and gardens, and wash their cars.

In a paper published Monday by Nature Sustainability, researchers compared rich elites’ drain on local supplies to other factors that deplete water resources and concluded that wealthy people are responsible for fueling urban water crises worldwide, “at least as much as climate change or population growth.”

They say that in the last two decades, more than 80 major cities worldwide have faced dire water shortages, everywhere from Miami to Tokyo and São Paulo to London. “Urban water crises can be triggered by the unsustainable consumption patterns of privileged social groups,” they write.

More than a billion people are estimated to be impacted in the coming years—the economically disadvantaged most of all. The United Nations has said that up to 2.4 billion people could face water shortages by 2050, almost 1 billion more than in 2016. Managing urban water systems has therefore become one of the most urgent societal challenges, and the authors note that projections of future drought and water demand suggest “an alarming risk of water crisis for many, if not most, cities across the world.”

With that in mind, few water uses sound as cartoonishly profligate as pumping disproportionate amounts into large swimming pools, spraying it on vast well-manicured lawns, and using it to make a car’s wheels shiny.

AN EYE-OPENING DEEP DIVE

The authors argue that perhaps no city proves this point better than Cape Town, South Africa—their case study where, for the period they examined, the wealthiest residents use 50 times more water than the city’s poorest did. They write that elites’ water use was largely for matters less life-or-death than staying hydrated, flushing the toilet, or cleaning oneself.

Most of the water consumed by privileged social groups (elite and upper-middle income) is used for non-basic water needs (amenities), such as the irrigation of residential gardens, swimming pools, and additional water fixtures, both indoor and outdoor. Conversely, most of the water consumed by other social groups (lower-middle income, lower income and informal dwellers) is used to satisfy basic water needs, such as drinking water, hygiene practices, and basic livelihood.

The “most striking” takeaway, the authors go on to say, was the total amount of water being consumed. Despite representing less than 14% of Cape Town’s population, the wealthiest residents used more than half the water consumed by the entire city. Meanwhile, the poorest people—who account for 62% of the population—consumed just 27% of the water.

Setting aside which use it’s even ultimately put to, the rich also have access to water that underprivileged groups lack, sometimes just miles away, thanks to the stark socioeconomic inequalities that exist in cities. The wealthiest people can buy, or simply claim, access to private water sources, equipping them with a special supply to tap in the event of a shortage.

In Cape Town’s case, the wealthier groups dug private boreholes to access groundwater to supplement their public water access, and then relied on those supplies when Cape Town experienced a near “day zero” event in 2018, threatening the city’s long-term water resources.

The study’s model, the researchers say, can be equally applied to water use in other big cities, and demonstrates how, in a scenario like Cape Town’s, overuse by the richest impairs water availability more drastically than if the entire population grew by 2%, or there was even a 2-degree Celsius (or 3.6-degree Fahrenheit) increase in temperature that reduced runoff water (which is necessary to replenish groundwater) by 10%.

They conclude that trying to solve the planet’s urban water crises without factoring in socioeconomic inequality leads to “technocratic solutions that are likely to perpetuate the same logic” that “contributed to the water crisis in the first place.”