The woman running 40 marathons in 40 days

Ultra-runner Mina Guli winced in pain in the middle of a cow paddock. Bandages wrapped around her beaten feet, she contemplated the "holes" where her toenails used to be.

She was back in her native Australia, but emotionally Ms Guli felt a long way from home.

Why am I doing this, she asked herself, of her attempt to complete 40 marathons in 40 days across six continents.

But Ms Guli resolved to work through the pain. She laced up her running shoes, pulled on her shorts and shirt, and "got the miles done".

"It wasn't a pretty day, there were lots of tears but I got through it," Ms Guli tells the BBC. "I don't run because I enjoy running, I run because I want to raise awareness about water issues."

The lawyer-turned-conservationist is nearing the end of a 1,687km (1,048 miles) journey designed to highlight the amount of water used in consumer goods.

"Only 5% of our water that we use is in our household consumption - the rest is in our 'invisible water footprint'," says Ms Guli.

She has run her marathons along the Colorado River in the US and Mexico, the Amazon River in Brazil, the Murray River in Australia, the Yangtze River in China and the Nile River in Egypt. She is due to finish the final leg on Monday along the River Thames in London.

Last year, Ms Guli, 46, finished an even longer odyssey spanning seven continents. She says the extensive distances and limited recovery time take a toll on her body, no matter how meticulous her preparation.

"I look a bit like an old granny after running the first couple of kilometres," she says.

"When I get up in the morning there's a lot of grimacing, a lot of hobbling. I've taken to doing the first couple of kilometres by myself because I don't want my (support) team to see how badly I'm hurting."

Rest is rare to keep the relentless pace, and when she is not running a lot of time is spent flying or driving to the next destination.

Along the way she has met with a range of locals - including indigenous leaders, tourism operators and farmers - to talk about the water issues they face.

The United Nations predicts that by 2025, 1.8 billion people will be living in countries or regions with water scarcity. Population growth, poor governance, pollution and climate change are cited as contributing factors.

Ms Guli says she is motivated by spreading a simple message: that many countries use water faster than nature can replenish it. In 2012, she founded Thirst, a global charity to educate young people on the topic.

"The thing that I draw upon when the going gets tough is the next generation," she says.

"I want a world where there is enough water for everyone forever."

Ms Guli says she will celebrate completing her achievement with ice cream.