Shippers must furnish the commission with a copy of steamship company's confirmation of space reservation to cover shipments for water movement. When shippers, consignees, rail or water carriers forward merchandise or commodities to be handled over the Port facilities without having previously made arrangement for the handling or storage of same, it is optional with the commission management as to whether such business shall be accepted or not, and the commission will not be responsible for any rail or steamship demurrage which may accrue under these circumstances.