70 ILCS 2605/20
Any channel or outlet constructed under the provisions of this act which shall cause the discharge of sewage into or through any river or stream of water beyond or without the limits of the district constructing the same shall be of sufficient size and capacity to produce a continuous flow of water of at least two hundred cubic feet per minute for each one thousand of the population of the district drained thereby, and the same shall be kept and maintained of such size and in such condition that the water thereof shall be neither offensive or injurious to the health of any of the people of this state; and before any sewage shall be discharged into such channel or outlet, all garbage, dead animals and parts thereof, and other solids shall be taken therefrom, and said district shall, at the time any sewage is turned into or through any such channel or channels, turn into said channel or channels not less than twenty thousand cubic feet of water per minute for every one hundred thousand inhabitants of said district, and shall thereafter maintain the flow of such quantity of water.
70 ILCS 2605/20