Water in your diesel fuel will cause your engine to run as if starving for fuel, even with a full tank. Fortunately, modern diesel engines routinely come equipped with fuel-water separators that trap the water in a collection bowl at the bottom of the separator. When you drain water from your fuel, a small amount of fuel will drain with it, meaning you must dispose of the water properly. Draining this bowl only takes a few moments and helps to ensure your continued operation.
Place a covered plastic bucket beneath the drain on the bowl at the bottom of the engine's fuel-water separator.
Open the valve on the bottom of the glass bowl at the bottom of the fuel-water separator. Depending on the manufacturer, your separator may have a petcock-type valve that you open by unscrewing it, or you may need to open it by pushing upward on the valve. When you open the valve, the water in the bowl will drain into the bucket.
Close the valve on the fuel-water separator when the bowl has emptied. Keep the fuel-contaminated water in the covered bucket until you return to shore.
Deliver the fuel-contaminated water to an approved facility---usually a fuel dock---for disposal. Note the fact of the delivery in your vessel's log, including the date, the amount of contaminated water delivered, the place to which you delivered it, the time you delivered it and which employee of the disposal facility accepted the delivery.