A system for separating water from crude oil includes a bulk-storage tank for storing unrefined crude oil, a first pipe for delivering water separated from crude oil in the bulk-storage tank to a containment system, a second pipe for delivering crude oil to a shipping system, a first valve for controlling flow in the first pipe, a second valve for controlling flow in the second pipe, and a control system for controlling operation of the first and second valves. The control system has a control device for controlling the first and second valves, an acoustic sensor array mounted on the first pipe for sensing a sound pressure level during flow of water through the first pipe, means for comparing the sensed sound pressure level with a predetermined sound pressure threshold level characterizing flow of oil-water mixture through the pipe, and a control device for closing the first valve and opening the second valve when the measured sound pressure level reaches the sound pressure threshold level.