Safe drinking water sends children (especially girls) back to school, empowers women, improves community health and fosters economic development. (1)

In just one day, 200 million work hours are consumed by women collecting water for their families. This lost productivity is greater than the combined number of hours worked in a week by employees at Walmart, United Parcel Service, McDonald's, IBM, Target, and Kroger. - water.org

Without clean water and sanitation, it is impossible to address poverty, hunger or AIDS.

The World Health Organization summarizes this way. (2)

When water comes from improved and more accessible sources, people spend less time and effort in physically collecting it, meaning they can be productive in other ways. It can also result in greater personal safety by reducing the need to make long or risky journeys to collect water. Better water sources also mean less expenditure on health, as people are less likely to fall ill and incur medical costs, and are better able to remain economically productive. 

With children particularly at risk from water-related diseases, access to improved sources of water can result in better health and therefore better school attendance, with longer-term consequences for their lives.

(1) "The Facts About The Global Drinking Water Crisis"

(2) http://www.who.int/mediacentre/factsheets/fs391/en/