CHARLESTON, S.C.—Having provided clean water solutions to the world’s largest natural disasters—including the South Asian tsunami, Hurricane Katrina, the China earthquake and Myanmar cyclone—engineers at Christian nonprofit engineering relief and development organization Water Missions International know that the worst in Haiti may be yet to come. “For our team, the race against the clock in Haiti has moved from mere survival to preventing deadly diseases associated with contaminated water and sewage,” said chemical engineer...