Around 315,000 children under-five die every day from diarrhoeal diseases caused by dirty water and poor sanitation. That's 900 children per day, or one child every two minutes.

Every year, around 60 million children are born into homes without access to sanitation.
(UNICEF, 2006 - Progress for Children)

For every $1 invested in water and sanitation, an average of at least $4 is returned in increased productivity.
(Hutton, Global costs and benefits of drinking-water supply and sanitation interventions to reach the MDG target and universal coverage, WHO, Geneva, 2012: page 4)