Mich. Comp. Laws § 290.644a

Sec. 4a. (1) A storage tank at a retail outlet shall be periodically tested by the retail dealer to insure that the tank does not have water or water-alcohol at the bottom of that tank in an amount greater than 2 inches. If there is more than 2 inches of water or water-alcohol at the bottom of the storage tank, gasoline, diesel fuel, biodiesel, or biodiesel blend shall not be sold to a consumer from that tank until the water or water-alcohol level is reduced to a level of less than 2 inches. (2) Adequate testing supplies, as determined by the department, shall be maintained at the retail outlet and shall also be made available to the department to determine the water or water-alcohol level in the storage tank.