Mexico City ? The numbers behind the world’s water crisis are daunting.

About 1.1 billion people lack clean drinking water, causing diseases that kill 3.1 million people a year. And 1.7 million deaths could be prevented with better sanitation.

Some of those attending the fourth World Water Forum in Mexico City focused instead on smaller numbers, like the average distance women in developing countries walk each day to fetch water: just under 4 miles.

Simple solutions can help, experts said Sunday. In Morocco, a World Bank project that moved water taps closer to villages increased school attendance by girls in six provinces by 20 percent over four years.

This and other projects under discussion here require a fraction of the cost of other solutions, like big dams.

There are other small numbers, like three: the estimated percentage of Africa’s hydropower potential that is used – compared to about 75 percent in Europe.

A majority of Africans lack regular electricity, preventing them from operating pumps to extract water from wells.

Massive hydroelectric dams could fix that, some say.

Haoua Outman Djame, water minister of Chad, said: “Africa must invest in water and hydroelectric infrastructure in the long term to eradicate poverty.”

Large dams can also be easier to maintain than small ones, said Gerald Galloway, a civil engineering professor and visiting scholar with the U.S. Army Corps of Engineers.

“We’ve seen that when you have lots of them (dams), they’re not easy to inspect and the specifications tend to be not quite at the same level as those for large dams,” Galloway said, referring to the United States, where four small, older dams burst in the last year.

Others disagree.

“It’s going to be all the problems with big dams revisited,” said Jamie Pittock, director of the World Wildlife Fund. He said that with big dams or irrigation projects, water doesn’t reach small, remote farms.

Instead, Pittock’s group is promoting the restoration of thousands of small, community earthen dams dating as far back as the 13th century.