The Mississippi-Rideau Source Protection Region is made up of two Source Protection Areas – the Mississippi Valley Source Protection Area which is made up of the lands that drain into the Mississippi River (also called the Mississippi watershed) and the Rideau Valley Source Protection Area which encompasses lands that drain into the Rideau River (the Rideau watershed). All or part of 31 municipalities fall within the Mississippi-Rideau Source Protection Region.

About three quarters of the population of the region live in an area that is serviced by the 12 municipal drinking water systems that are the focus of the Mississippi-Rideau Source Protection Plan.