Requires the Secretary of the Army, through the Chief of Engineers and at the request of a state in which a federal reservoir operated by the Secretary is located, to calculate the aggregate withdrawals of a non-federal entity by subtracting any return flow. Defines "return flow" as a discharge that flows directly or indirectly into a reservoir from a wastewater or water supply system in accordance with applicable federal law, excluding a discharge of storm water that would have flowed into such a reservoir in the absence of a discharge by a non-federal entity.