Welcome to Number Crunching With OZY. In this occasional series, we ask businesspeople, experts, celebrities and thought leaders to discuss a single number that is most important to them. This time: Scott Harrison, founder and CEO of Charity: Water.

Today, there are 1 billion fewer people living in extreme poverty than in 1980 — less than 10 percent of the world’s population, compared to more than 40 percent four decades ago. The swift improvement is largely due to rapid economic growth in East and South Asia. But the remaining population of the global impoverished is the hardest to reach — mostly in rural areas of sub-Saharan Africa — making it more necessary than ever to identify and prioritize the interventions that can do the most to help.

And it turns out that one of the most important factors to focus on may come from a surprising place — not health care, nutrition, education or economic growth, but time. The time spent on arduous domestic duties in developing regions can sink hundreds of hours per month for women and girls, which could otherwise be spent productively. In fact:

In Africa alone, women spend a cumulative 200 million hours on average every day collecting water.

That number comes from the 2015 Human Development Report from the United Nations Development Programme, and is cited by Scott Harrison, founder and CEO of the nonprofit Charity: Water, as one of the most important numbers shaping his organization’s approach to providing water in developing regions. Gender is intrinsically linked to the issue of wasted time: Globally, women spend more total time working than men. Although men perform almost twice as much paid work as women, the opposite is true of women’s unpaid work by a factor of three.

Women and girls are responsible for water collection in 80 percent of households.

This unnecessary time sink in chores such as fetching water means that there are “markedly different opportunities and outcomes for human development” for men and women, says the UNDP report. Women and girls are responsible for water collection in 80 percent of households, according to UNICEF data. This “poses impediments to [women] pursuing other activities such as education, paid work, participation or leisure,” continues the UNDP. In some parts of rural Africa, women spend up to eight hours per day collecting water, notes Harrison.

It’s not just the opportunity cost of hours wasted by women and girls that makes water such an important and “fundamental” issue for development and gender equality in developing regions, says Evariste Kouassi Komlan, UNICEF senior adviser for water, sanitation and hygiene. In addition, women and girls disproportionately spend a “great deal of time each day queuing for public toilets or seeking secluded spots to defecate, [also] putting them at risk” of gender-based violence, he says.

Of course, gaining a better understanding of the problem is only the first step. While 663 million people are drinking dirty water today — down from 1 billion a decade ago — “the hard work really begins now,” says Harrison. Many of those who got access to clean water in the past 10 years were based in urban areas, while those remaining “are living in these remote rural areas,” he says, making small, localized solutions that minimize the distance to travel ever more important, such as drilling wells, building rainwater harvesting systems or tapping mountain streams.

So as the international development community continues to experiment with the most effective ways to be altruistic — the old adage about giving someone a fishing rod rather than a fish — maybe it’s worth considering whether instead of putting cash, school books, medicine or even fishing rods into people’s hands, most fundamental of all could be time.