Michigan derives its water from the Great Lakes Watershed and a portion of this water is withdrawn for public supply.  According to the Michigan Department of Environmental Quality, public water supply refers to the diversion, treatment, and distribution of water for residential, public, commercial, and industrial consumption.  It generally excludes agricultural, thermoelectric, and self-supplied water for industrial use.  This chart illustrates the source of these withdrawals in 2006, the most recent year of verified data.   According to this chart, water from the Great Lakes were used for 76 percent of Michigan’s water supply withdrawals in 2006, ground water was used for 23 percent of the withdrawals and surface water was used for 1 percent.

The vast majority of Michigan’s public water supply was derived from the Great Lakes in 2006, and only small fractions of the total water supply was derived from surface water (streams, inland lakes, etc.) and groundwater.  However, these proportions change when looking at southeast Michigan.  The chart below illustrates the greater reliance on Great Lakes water for public supply in the 10-county region of southeast Michigan.  These counties draw 91 percent of their public water supply from Great Lakes sources, compared to the statewide percentage of 76 percent. A smaller percentage of southeast Michigan’s withdrawals come from groundwater (7%) than the state as a whole (23%).  Reliance on surface water is small and relatively equal to the state at large.

This chart illustrates the disproportionate withdrawals of Great Lakes water by the 10 counties that make up southeastern Michigan. St. Clair and Wayne counties rely the heaviest on public water supply withdrawal.  Public water supply withdrawal data in southeast Michigan are thus characterized heavily by the Detroit Public Water Supply System’s intake plan.  By extension, it is important to note that a county’s withdrawal does not necessarily reflect its consumption.

This chart illustrates the 10-county region’s reliance on surface and groundwater sources for public water supply.  While surface and groundwater withdrawals are not negligible in southeast Michigan, they are dwarfed by Great Lakes withdrawals.  Oakland County withdraws the greatest volume of water from groundwater sources at 22.92 MGD. Washtenaw County withdraws the greatest volume of surface water for public supply at 12.58 MGD.

This chart plots the total volume of public water supply withdrawal by the top four counties in southeast Michigan from 1997 through 2006.  Total withdrawal levels have varied somewhat over time, but not substantially.  Wayne County displays a visible decline during this time frame and, despite strains associated with sprawl and population dispersal in this time span, withdrawals for public water supply have not grown in these counties.

To view information related to pollution in the Great Lakes check back with Drawing Detroit.