How was value determined:

1. The regional value for water water supply was transferred from one peer-reviewed study of the impacts of water based activities in South Dakota and Wyoming (Piper 1997).
2. This value (per irrigated acre) was multiplied by the acres of irrigated land and divided by the surface area of water in the West Michigan policy region (National Agricultural Statistics Service 2002).

Value estimate limitations:

1. The value represented here accounts for the quality of water for agricultural irrigation. The value used here may also include a wetland's ability to recharge an aquifer and replenish groundwater supplies and streamflow.
2. Water supply value needs to include other alternative uses such as public, domestic and industrial uses of water.
3. Water supply value may also depend on the quality of water.