What's worse: water in your diesel or diesel in your water

I had a nightmare last night. It went something like this: we're at the fuel dock and I'm down below looking for my credit card when my buddy who's helping out yells from the cockpit: Hey! So, which one is the water tank? The one on the right or the on the left?

I want to say the one on the "starboard" side but I don't want to sound condescending by pulling out "nautical terms" so I respond by saying: "on the right". You see... The issue here was that he was facing the stern!

So I woke up troubled with this question: what's worse? Pouring water in your fuel tank or diesel in your water tank?

I am sure the ramifications of either extend beyond what I can easily think of right now (after all, I haven't had my coffee yet!) so I thought I'd pose the question here.

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Hi Franc,

You have just confirmed my decision to fill the fuel tank today. I am here in Boston and have been doing work on installing a generator and have been waiting to fill the tank because of the need to drill a hole in the tank to make a connection for the generator. I am worried about condensation though!! I got into my lazerette and felt it on the hull. So seeing your post here is a reminder for me. I think getting water out of the diesel fuel would be easier then getting diesel out of the water tanks. But then any problem/project on a boat is a major pain in the butt. My water tanks are fiberglass tanks.

Onboard Topaz
I instead of a new hole in the tank just put a "T' into the fuel line. The generator will be fed by the same pick up as the engine would be. You'll need a T in the return line as well.

s/v Veranda
So did you get fuel in the water?...I had a similar thing happen to my prized 79 classic MGB..took it to a service station for a tune up and fluids...well the service people put oil in my took all I had not to slap them. My My My.
I had a similar thing happen to me one time in Newport.
We had arrived in Newport Rhode Island aboard American Promise in the early AM, and all the crew were busy cleaning up the boat. As the forward crew were scrubbing the deck, I told the boat's Midshipman Executive Officer (XO) to also fill one of the water tanks so I could take a shower. The XO was familiar with the tankage system on the boat (4 water & 4 fuel tanks)
I also had the generator running to warm the water for my shower.
While I was in the shower, I could hear that the generator had suddenly stop.
I yelled out,"did someone stop the generator?". "NO", was the reply.
I quickly finish my shower, look at the instrument panel, go into the machinery space,look at the RACOR, and see it's full of water!
I walk up on deck, see the Plebe (4th class Midshipman (Freshman)) with the freshwater hose in the fuel tank fill.
You can imagine what all hands lecture I proceeded to rip the XO a new culo. The XO had decided to delegate his task (true sign of leadership).
What were the chances with 4 water tanks to fill that they would select 1 of 4 fuel tanks to fill up with water while the generator was drawing from that particular tank?!!!
OK, here's the evaluation. Water in the fuel tank- not so bad. It happens all the time. Water is heavier than fuel, so it all goes to the bottom. (there is water in everyone's fuel tanks, always) We can pump the water out, and keep changing racors.
It get's worse:Getting water past the RACOR, and past the secondary fuel filter and into the fuel distribution pump: BAD.
Yes, we pumped the 60 or so gallons of water out of the fuel tank, and took the waste water to the large water/oil separator facility at NAVSTA Newport, swapped out a few RACOR filters (there's a scrubbing system on American Promise with a pair of very large RACOR filters and an electric pump to move fuel to different tanks) , and the main engine and genset have dual RACORs for changing single RACORs while operating off the second redundant RACOR (great system, good upgrade for all boats). Totally disassembling the tube components to the genset fuel system and flushing them in buckets with fresh diesel was also another precautionary effort.
With a new secondary fuel filter, and some open injector lines to rotate the genset to wast about a pint of diesel before reconnecting the injectors and restart the genset.
The genset ran good for a while, but it was an old Perkins hybrid system and about halfway to Bermuda it died while it appeared to be making crankcase oil (oil level on dipstick got higher and the oil became opaque (water in oil).
The seals had blown out between the injector distribution pump and the drive gear where the primary cause for this was the water not being a good lubricant for the shaft going through those seals. Diesel fuel is the lubricant for the distributions pump gearing.
Had this been a quickly discovered water accident to the fuel system, and the RACOR water alarm sounded (or had been listened to in this case), the genset would have died for some other reason in the future. The water would be dealt with without much duress.
The other side of the coin is that when a water tank gets filled with fuel, then that tank is ruined for drinking water. Then you have two options. Either you now have a new fuel tank, or you rip it out and install a new water tank (and water lines, pumps, etc...)
The water tanks on American Promise are immensely difficult to access, so AmPro would then have 5 fuel tanks if we contaminated a water tank...
American Promise was built to sail non-stop around the world, hence the reason for the numerous fuel and water tanks.
Franc, good question and one issue I hope I never have to deal with. Water in a diesel engine can kill it. Piston rods bend and break before you realize you can't compress water. Diesel in your water tanks will take forever to clean out. Based on the cost of and aggravation of cleaning or installing water tank versus rebuilding or replacing a diesel engine, I'll opt for diesel in my water tank. A good reason to never trust anyone other than yourself to fill a tank, water or fuel.
Have a Merry Christmas!



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