As intense heatwaves grip many parts of the world, it’s hard to imagine why someone might deliberately avoid drinking water — but that’s exactly what some women and girls are doing in India.

Across the world, 2.3 billion people don’t have access to basic sanitation, and almost 892 million people still practice open defecation — about 600 million of whom live in India, according to the World Health Organization (WHO).

Open defecation puts women and girls at risk, as finding hidden places to defecate increases their chance of rape and attack. It also makes managing menstruation difficult and it perpetuates a cycle of poverty.

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So girls and women avoid drinking and eating so they can avoid having to urinate or defecate.

"Sometimes, I drink less water because the spot we use to go to the toilet in the open is filled with notorious boys. I am afraid to go there," a 13-year-old in Delhi, India, told the BBC.

The young woman only visits the spot once a day with other women early in the morning or late in the evening.

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"They intentionally dehydrate themselves — and this can have serious effects if it's really hot or if there is a heatwave," Gulrez Shah Azhar, a researcher at nonprofit Rand Corporation, told BBC.

Azhar said that women were much more likely to die from a heatwave after studying a heatwave in the western city of Ahmedabad in 2010.

He explained that women who stay indoors face less of a risk during a heatwave, but lack of basic sanitation, unreliable cooling systems like ceiling fans, indoor cooking, and traditional Indian attire for women can still cause severe heating issues for women inside.

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Women in Ahmedabad are also often tasked with domestic duties.

"It gets difficult to use the toilet. We wait for the men to go first," Damini Rameshbhai Marwadi told the BBC. "As women, we must first complete the household work. During the summer, I ended up getting jaundice because I was restricting myself."

Azhar pointed out "a culture of silence that surrounds women's sanitation issues that leads to death."

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He noted that dealing with equality issues and women’s rights would be a long-term solution.

Researchers have warned that heatwaves could eventually become so extreme in South Asia that some regions would be too hot for human survival. India, Pakistan, and Bangladesh would be the worst affected, according to the scientists.

Needless to say, it is not feasible for women and girls to continue to restrict their water and food intake.

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Open defecation is a leading contributor to the spread of fatal diseases, malnutrition, missed school days, gender disparity, environmental contamination, and the perpetuation of extreme poverty.

Ending this practice means prioritizing handwashing, education and behavior change programming, as well as waste treatment systems through financial resourcing and political will.

"But access to an indoor toilet and clean drinking water remains paramount," Azhar told BBC.