MBYO, Rwanda — They awoke early and gathered along a plot of land here in this Rwandan village made up of a handful of homes. Together, they began hacking away at a grass-bare patch with long-handled garden hoes. The mission: Dig a drainage ditch alongside a row of homes that had been continuously flooding during rains.

Scenes like this one were playing out across Rwanda on this Saturday — a monthly day of service known as Umuganda.

The premise is simple and extraordinary in its efficient enforcement: Every able-bodied Rwandan citizen between the ages of 18 and 65 must take part in community service for three hours once a month. The community identifies a new public works problem to tackle each month.

“We never had Umuganda before the genocide,” said Jean Baptiste Kwizera, 21, wiping sweat from his brow as he took a break from the project here in Mbyo, about an hour’s drive from Kigali, the capital.