When 15-year-old Mellan Chansa started menstruating, her biggest fears while venturing into the bush to change her sanitary towel were snakes and peeping boys.
She had no choice but to risk encountering both, since her school in Bunda Chunsu village, northern Zambia, had no proper toilets, forcing Chansa and her classmates to use the surrounding grasslands instead.
The school once had a latrine but it now stands abandoned at the side of a soccer field, covered with burnt grass. The students refused to use it due to constant overflowing.
"I almost cried when I came here and saw the facilities," head teacher John Zulu told the Thomson Reuters Foundation. "Girls would go to the makeshift toilet and run out almost half-naked because they would find a snake lurking there," he said, sitting in his small office overlooking the schoolyard where a Zambian flag on a pole was flapping in the wind.
For girls, especially those who, like Chansa, had started their periods, using the bush as a toilet meant a lack of privacy and dignity. "Apart from snakes, the boys used to peep at us and sometimes mocked us, which made us girls frustrated, so I rarely came to school when I was menstruating," Chansa said. Universal access to clean water and sanitation is one of a raft of development targets that world leaders are due to endorse later this month.
But poor countries like Zambia will be hard pushed to achieve the objective, experts say. The southern African country has managed to nearly halve the proportion of people practising open defecation to 16 percent in 2012 from 26 percent in 1990.
Only about three in five Zambians have access to toilets including pit latrines or public toilets, according to the United Nations. Only 45% of schools have toilets.
The World Bank says Zambia loses $194 million, equivalent to 1.3% of its gross domestic product, every year due to illness and premature death from poor sanitation.
For schoolgirls, a lack of toilets often means missing lessons or pulling out of school altogether. Menstruating girls around the world miss up to 20% of their classes if their schools have no toilets, the U.N. children's agency UNICEF says.
Governments in countries with poor sanitation often do not see providing schools with toilets as a priority, says the charity WaterAid, which built toilets for the school in Bunda Chunsu three years ago. The simple concrete buildings have transformed life for both students and teachers.
"It was difficult when six or eight girls were absent (every month)," Mutinta Handondo, the only female teacher at the school, told the Thomson Reuters Foundation.
"It meant repeating the same topic for some time, so our learning was a challenge," she said. Another benefit has been fewer cases of child marriage.
Handondo said parents used to argue that it was better for girls who had reached puberty to get married than go to a school where they had no dignity. Although Zambian law forbids marriage below the age of 21, more than 40% of girls are married before they turn 18, according to the United Nations Population Fund (UNFPA).
"By the time the girl finishes her menstruation you just hear that she's married," Handondo said. "We are having a lot of problems because of that." Once married, girls often become pregnant and drop out of school completely.
Girl brides not only miss out on their education but are at greater risk of life-threatening complications in pregnancy and childbirth because their bodies are not fully developed, campaigners say.
Hidden from curious looks behind a small hill, the toilet for girls in Bunda Chunsu includes a washroom where they can clean themselves and change when they are menstruating.
"When toilets were built I felt good, I was very happy," said Chansa, who would like to be a teacher one day.
After hearing about the new toilets, some girls now walk up to 10 kilometres (6 miles) to attend the school in Bunda Chunsu, said head teacher Zulu. Before the toilets were built, poor attendance meant only a small number of 16-year-old girls qualified for secondary school, he said.
Although the same number of girls and boys finish primary school in Zambia, gender parity in secondary education has fallen to 0.86 in 2010 from 0.92 in 1990, primarily because of a high dropout rate for girls, according to the United Nations.
For a long time, the majority of Bunda Chunsu students who went on to secondary school were boys. But last year, girls were in the majority. "Access to safe, reliable, clean, private sanitation and water and hygiene is really a question of girls' and women's welfare and girls' and women's rights," Seemin Qayum, UN Women policy advisor on sustainable development, told the Thomson Reuters Foundation in a phone interview from New York.
"If we're thinking about keeping girls at school, we need to do a lot of work on the sanitation issue and make sure that there are clean, private, safe and separate facilities for girls at schools. I think this is fundamental," Qayum said.