On April 30, along the paved banks of the Thames in London, Australian ultra runner and water advocate Mina Guli slogged the final steps of her ambitious run along six of the earth’s most ailing rivers. In the course of her Run4Water expedition, which began in Las Vegas on World Water Day, Guli ran 40 marathons in 40 days—1,049 miles—toiling beside the Colorado, Amazon, Murray, Yangtze, and Nile Rivers before finishing in London.

The odyssey aimed to highlight the worsening global water crisis and, through support garnered along the way, to convey to the United Nations the commitment of the world’s citizens to solving its most pressing predicament. According to a 2015 UN report, the world’s demand for water will outstrip its supply by 40 percent by 2030.  

“We can only solve this problem by bringing together consumers, producers, farmers, manufacturers, and policymakers around the world,” Guli, 46, says. “It’s too big, too severe to just sit by until we don’t have any water to drink anymore.”

Guli, who last year ran 40 marathons across the driest deserts on each continent, took to the rivers to unite such people through conversation, shared stories, and the simple act of running. She spoke with farmers, locals, Aboriginal elders, and water experts to experience firsthand what water means to those who are most intimate with its preciousness. Most days, kids and families joined her for a few miles by the river. She milked cows, floated to school with Amazonian children, and explored ancient water measurement devices along the Nile. 

“The thing that really gets me excited is not the running part,” Guli explains. “It’s the opportunity to see firsthand the implications of water scarcity and water issues. It’s the incredible people doing amazing things.” 

And yet, the running had to be reckoned with. The Amazon was wet and muddy, Egypt a broiling 113 degrees, the Yangtze assailed with deluges of rain. Early into her Murray River run, just a third of the way into her expedition, Guli was already suffering from shin splints and generally battered, blistered feet. “It’s wreaked a lot of havoc on my body,” she laments. “We all said RIP to the Amazonian toenails, disappearing day by day. I lost another one last night.”

The days were long and grueling, beginning at 4:30 A.M., and between photo ops and connecting with locals, she often didn’t finish the day’s final miles until 9 P.M. “It’s a constant tension all day between getting miles done and wanting to tell stories,” Guli says. “I get way too excited about learning about water. Every day I wake up and say I’ve got to make sure I’m back to camp by 4 P.M. so I can do some proper recovery. But Mina gets too distracted by other things. Oh, let’s just run over here! Oh, look at that!” 

The fact that Guli doesn’t actually like running didn’t help, either. By her own admission, she’s no world-class athlete. But, like the best warriors, she’s also incorrigibly stubborn. At 22, she was pushed into a pool and broke her back. Doctors said she’d never run again. So, she set out to prove them wrong, gradually rehabilitating through swimming, biking, and eventually ultra running. 

Guli’s work in water advocacy came later. She grew up in Australia during a decade of drought and had always figured she did her part to save water by taking short showers and turning off the tap while brushing her teeth. 

“What I hadn’t realized until a couple of years ago is that that represents a very small part of my daily water footprint,” Guli explains. “Ninety-five percent of the water we use every day goes into the things that we use and buy and consume.” 

In 2012, astounded that she’d been so uninformed, Guli founded the nonprofit Thirst, which works to change the way we think about and consume water, and has so far educated some half a million kids in China who, Guli observes, immediately began to change their behavior as consumers. Last year, Guli was named one of the “World's Greatest Leaders” by Fortune.

Back on Australia’s Murray River, Guli reflected on her expedition experiences and what they’ve taught her about the water cycle. She’d run beside the dammed, over-allocated Colorado that river guides told her was diminishing year by year, along with its reservoirs. Sitting atop a 200-year-old tree in the Amazonian jungle with a local water expert, drenched in the forest’s exhalations, she’d witnessed the “flying river” flowing like tufts of smoke above the grounded river below it, blowing down to other parts of Brazil. Rampant, illegal deforestation, though, had disrupted that cycle’s flow and helped spawn drought in places like Sao Paulo, where in 2015 the crisis got so bad that Brazil’s army staged simulations of a mass uprising at the local water utility in preparation for what they believed was the inevitable. 

“Even in places where we think there’s loads of water, there isn’t always,” Guli says. “We are fundamentally affecting the ecosystem through acts that we may not always realize have a water impact.”

The question then becomes what can we do? On the grander scale, Guli says, people and organizations in all sectors need to come together to find solutions, and that requires a lot of conversation, education, and active nudging. As individuals, though, we can make better consumer choices. She encourages everyone to “understand where your stuff comes from and reward companies that use water more efficiently” by choosing their products over those of more wasteful companies. 

Guli hopes her run will bear fruit and expects to announce a coalition of organizations uniting under a pledge to work out solutions and use water more sustainably, like the farmers in Australia who sow their fields with absorbent gypsum that holds water in the soil. After her run, Guli visited the UN headquarters to hand-deliver the flag she’d carried along all six rivers. The blue flag, which reads “6 Clean Water and Sanitation” to signify the UN’s sixth sustainable development goal, bore the signatures of individuals and companies she’d convinced along the way. The message: We care, and we’re committed to doing our part.

First she had to run the world’s rivers to get there. Most days on that journey, she just wanted to sit and have a cup of tea, read a book, revel in the natural, imperiled beauty all around her. But, she says, she didn’t have that luxury. 

“We have a big water crisis,” Guli reflects, “and we need to do something to solve it or there will be no sitting beside beautiful rivers and enjoying the scenery. I want to make sure that the next generation has the opportunity to do that, and that means there will be a lot of days when I don’t.”