CHILD’S PLAY IS THE UNLIKELY SOLUTION to a sub-Saharan public health crisis: the high incidence of disease transmitted by dirty water. With each rotation of a PlayPump’s colorful merry-go-round, children draw clean water from 330-foot-deep wells into 660-gallon storage tanks that feature space for advertisements and public health messages about such concerns as HIV/AIDS prevention and proper hand-washing. The ad revenues fund the maintenance of the $14,000 system.