This week, you might see two young girls pictured on the side of London's buses, each hauling a jerry can of water that is more than half their weight.
Some 748million people around the world do not have access to safe water. That is one person in 10. Around the world, it is nearly always up to girls and women to hike treacherous paths to fetch water and carry that heavy burden home to their families.
Ze and Solo are best friends from the African island of Madagascar, whose job it is to get water for their families each day. Please follow here over the next four weeks as they share their stories and tell us what it means to them to be a girl.
WEEK 1: Emily's story
This spring I journeyed with my WaterAid team to the top of the red island - Madagascar - to four isolated communities perched 2,000 metres up in the highlands.
The rainy season had just passed, feeding small green luminous fields of rice and corn. We drove two hours from the nearest city down potholed roads, to a place of zebu cattle carts and tiny roadside shacks selling sugared flour patties, local yoghurt and strong, bitter coffee. Then we turned off and squeezed the car down a narrow track, bristling cacti scraping the sides, until an hour later it ended at the foot of a small mountain.
This is where we met Solo and Ze, two young girls whose daily lives are wrapped around the struggle to find enough water for their families. At first look it was impossible to imagine their small, battered feet making their way across large crevasses up an uneven, red mud path, five times a day to the small muddy hole that serves as a water source.
This is a place where people live day by day. The focus is survival. The girls dream only of good health and safe water.
It's all on the girls
Solo and Ze are bright young girls, chattering to other and turning the interview around on me, asking questions about my life, my family, my home. I was struck by Solo's gentle nature, she's shy but with a spark, and sat close to me.
Solo is the only girl in a family of six children, her brothers both younger and older than her. She left school last year, at 12, which she told us was her own decision, though clearly made out of a duty to her family.
Ze is third in a family of seven children and the oldest girl, making it her job to fetch water each day; she, too, has left school, because of her household duties.
In this village all domestic responsibilities fall to the girls, though their older brothers have finished school and younger siblings still attend. School is viewed as a route out of a farming life, a possible path out of poverty.
Women and men work in the fields. Boys attend school or farm. Cooking, cleaning, washing, and collecting water and firewood falls to the girls. This is usually shared among daughters, but in Solo's family, as the only daughter, it's all on her.
You could see subtle signs of the disparities between girls and boys everywhere. Small piles of photos decorated their homes' cramped interiors, documenting milestones and celebrations. But the images were always of the boys; girls rarely made it into the frame.
These girls are dedicated to their families and responsible beyond any girl of their age I'd ever met. We hiked to the water point with the girls, watching as they scooped water into their jerry cans, using their hands to clear scum from the surface.
The jerry cans hold nearly 20 litres of water. They are unbelievably heavy. I managed to move one, but there's no way I could carry it any distance. The girls laughed and told me that I'd be strong enough if I practised enough. I winced as I watched Solo hoist it up her small frame and onto her head.
The girls, of course, were matter-of-fact. This is their life. They speak of the future - of how a nearby water point would change their lives, allow them to return to the classroom, take away their stomach complaints. They are hopeful.
This summer, the Department for International Development has agreed to match donations to WaterAid's To Be A Girl campaign. With that help, we believe we can change their lives.
The Department for International Development has agreed to match all donations received this summer for WaterAid's campaign, To Be A Girl. We aim to reach 130,000 girls with safe water and basic toilets to give them a better future. To learn more, please see tobeagirl.org.
Follow Emily Graham on Twitter: www.twitter.com/Emily__Graham