Half a billion litres. Halfway to a billion. It is a big number, and big numbers can feel abstract. So here is what it really is. It is a glass filled at a kitchen sink in Kigali. A jerrycan carried home in time for school. A restaurant that opens on schedule because the tap works. A clinic with clean hands and clean instruments. Five hundred million litres is not a statistic — it is half a billion ordinary moments that used to be uncertain and now simply happen. Every litre

“Alain is a recent Civil Engineering Graduate who is about to complete his 6-months apprenticeship with the company in the Studies and...