This month, 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 748 million people around the world do not have access to safe water. That is one person in 10. It is nearly always up to girls and women to hike treacherous, winding paths to fetch water for their families, and carry that heavy burden home again.
Ze and Solo are best friends from the African island of Madagascar. This is the third in a series following them as they share their story of what it means to be a girl.
WEEK 3: ZE'S STORY
Zemiso Iarinirina is 12, but looks younger, with a big bright smile. Third in her family of seven children, she does not attend school, because it is her job to fetch water for her family. It is the first thing she does when she wakes, and the last journey she makes before she sleeps at night.
Ze with her family. WaterAid/Abbie Trayler-Smith
'I was seven when I started carrying water. My mother taught me, because otherwise I would lose water on the way. At the time I wasn't as expert as I am now with carrying water on top of my head, so it would all fall on me. It didn't take me that long to learn. It does feel heavy and gives me a headache. I started with a small bucket. It will get bigger as I grow up, but I get stronger every day, despite my size.
"I wake up and I go directly to fetch water. Afterwards I have my breakfast. I come with either my siblings or my friends to collect water. The pathway is very steep. And when I am in a hurry it's very dangerous. I fall. If there are snakes I have to go away from the pathway and I may slip. I carry a 20-litre jerry can. I balance it on top of my head. Sometimes I have to fetch water five times a day and when people are coming to help us in the fields, it's more, around seven.
"Solo is my best friend. We talk a lot when we are getting water. We are like sisters really. We look after each other.
WaterAid/ Abbie Trayler-Smith
Dirty, smelly water
"The smell of the water is so bad. In the rainy season the water becomes muddy, and the water is very dirty. Sometimes the ducks go in here and pollute the water and we have to drink from it.
"When we drink from this water, we suffer from diarrhoea. Yes, it gives me a bad tummy.
"Many people use the water and it gets dirty. Almost everyone goes there to collect water and get washed. Also, people use it for laundry and at that time the water is really, really, dirty. I use the water for laundry too and for washing ourselves. We wash in the field, near the water hole. I wait until no one is around. I am worried about my privacy, because I am shy.
"It's very hard to go fetch water. And I am always in a hurry, it's tiring. I feel so weak and overwhelmed, very weak. I have to collect water in the dark. At night, in the full moon, we can see. It's very hard at night, because you have to be cautious where you are putting your feet.
"Sometimes I get sprains and bruises, because I fall. In the daytime, you can think of something else or talk, but at night you have to focus on the pathway. It happens often that I go at night, as I am kept at the field.
'I want to go back to school'
"I no longer go to school. I started going when I was 11 but I stopped last year at grade 2 [when I was 12] because my parents were in difficulty, and needed me to go fetch water. I had no choice. I liked school very much, because I could learn how to write.
"I want to change my life now; I want to go back to school. I would like to learn more. I really want to be educated. I like writing. If I had the choice, I would like water to be close by. I believe my life would be different, because the water point would be so close and I would have time to go to school. And that will be a big difference. I will be cleaner, and I'll be healthier, as I can wash when I want."
The Department of International Development has agreed to match all donations received this summer for WaterAid's campaign, To Be A Girl, exploring how not having safe water or basic sanitation threatens the health, safety, education and future of girls in developing countries.
WaterAid/ Abbie Trayler-Smith