I used to run the company that made most of the oil/water separators used in a/c refueling. The units are designed to deliver fuel with less than 5ppm water. There is also (supposed to be) a shut off on the delivery side which stops delivery if fuel with more that 5ppm water is detected. Of course, 5ppm of water can accumulate over several refuels but it was always felt that the scavenging pumps would take care of most of the build up and tank draining during routine maintenance would clear the rest. I am now retired so I am not sure if this is still the standard for aviation fuel. I am a PPL so I am not familiar with the details of commercial a/c fuel systems.