Mary Chervenak's excellent summer adventure started on June 1 at the United Nations.
"I had so much adrenaline pumping, my legs were shaking," said the 39-year-old chemist from North Carolina.
Chervenak is one of 21 people from 13 countries who put their jobs and families on hold to run a relay around the world. By the time the runners finish back in New York this Tuesday, they will have covered more than 15,000 miles and traversed 16 countries in four continents.
The round-the-clock relay will be completed in 95 days. It is being sponsored by the Blue Planet Run Foundation, a non-profit organization that was founded five years ago and is dedicated to raising global awareness and money for safe drinking projects in the developing world.
Blue Planet has already funded more than 130 such projects in third-world countries. According to the World Health Organization, one in five people around the world lacks access to clean water and sanitation. As a result, waterborne diseases kill more people than AIDS, and nearly 2 million children die each year from diarrhea alone.
From New York, the runners headed to Boston, then through Ireland, Britain, France, Belgium and the Netherlands, each running 10 miles a day. During every hand-off, the runners pass a baton carrying their global water pledge and recommit themselves to making a difference by going the distance.
By the time the team crossed from Europe to Asia into Central Russia on July 4, team members were definitely feeling the effects of constant running. The unfamiliar food, less-than-ideal sleeping accommodations and lack of hot showers were taking their toll on the group -- not to mention the various scrapes, aches and blisters afflicting many in the team.
But in case any of the runners needed a reminder of why they were running in the first place, the effects of bad food and water sidelined a quarter of the team in China.
For one of the runners in particular, the relay's mission was intensely personal. Emmanuel Kibet, a professional marathoner from Kenya, grew up in a family of nine without regular access to clean water.
Traveling through Russia was one of the highlights of the relay for Kibet. He was a virtual star almost everywhere he went. Ordinary Russians regularly asked to have their photos taken with the Kenyan throughout the region.
His popularity was a revelation to Kibet, but not as much as the sight of Lake Baikal in Siberia, the largest source of fresh water on the planet. In fact, the lake contains 20 percent of all the fresh water on Earth.
When he reached the lake, Kibet ran into its freezing water in complete disregard of the cold temperature.
"When I see water like this, I feel like drinking it -- because water is life," said Kibet.
Another member of the team who has been personally affected by the global water crisis is Simon Isaacs. The 26-year-old native New Englander is taking time off from his job in Rwanda, where he helps develop programs aimed at expanding access to safe drinking water.
As he ran through the Gobi Desert, Isaacs contemplated how the possible effects of global warming could exacerbate the already dire water situation in certain regions.
"As the climate changes, Mongolia is one of those countries that will go from being a water-stressed country to a water-scarce country," said Isaacs.
Sunila Jayaraj, 29, never ran a mile in his life until he discovered "pledge runs" as a way to raise money for victims of his native India's devastating drought and flood cycles. Born in the semi-arid region of Kolar, Jayaraj is acutely aware of the devastating impact that lack of clean water can wreak on a country as densely populated as India.
"The population itself is a big crisis, and the water and the population make it worse," said Jayaraj. "Education and health -- everything is linked to the water."
But it wasn't all hardship. Japan's Taeko Terauchi and Canada's Jason Loutit started dating in France and got engaged in Russia.
When they made it to Japan, the couple stopped long enough to receive her parents' blessing. They then got married while running past Niagara Falls.
For them, the phrase "long-distance relationship" took on a whole new meaning.
The newlyweds and the rest of the runners are now in the home stretch. They've made it across most of the United States. Their excellent and very tiring adventure ends this Tuesday back where they started in New York.
ABC News' Mike Cerre and Suzanne Yeo contributed to this report.