NO SINGLE SOLUTION
In some countries, tap water is even more unsafe than pond water, with around 80 percent of Bangladesh's piped supplies contaminated by E.coli bacteria, said the report.
It urged governments to better inform people and encourage more household water treatment.
Providing piped water in cities could generate economies of scale, the bank said, urging greater private-sector involvement in urban water provision where recovering costs may be easier.
Researchers, decision makers and aid specialists are meeting in Stockholm for the annual World Water Week where they will focus on how to reduce waste in water use.
Water and sanitation improvements should be linked to health programmes to better tackle disease and malnutrition, said the World Bank report.
"Renewed efforts are needed to address those populations at greatest risk of death and disease due to inadequate water supply, sanitation and hygiene, which threatens human capital and economic development," it said.
