The Official Magazine of the Bluewater Cruising Association

Lessons Learned the Hard Way...Water in the Fuel Tank

Norm Cooper

Sarah Jean II
Saga 43
May 24th, 2015

Norm shares one more lesson learned while sailing: this time from Prince Rupert on the way to Haida Gwaii. When the Coopers were ready to depart from Prince Rupert, something did not go quite as planned.  This time, the lesson learned is about filling up the wrong tank with water.


We were about to depart the marina in Prince Rupert. We planned to stop at the fuel dock and then head off across Hecate Straight to Haida Gwaii. We had no watermaker at the time, so at the last moment I thought it prudent to top up our water tanks. We were moored stern in, not our normal practice of mooring bow in. I grabbed the dock water hose and started topping up the starboard water tank. It was already almost full so I was surprised how long it was taking to top it up. When I took a closer look, I found I had been filling a nearly empty diesel fuel tank! My heart sunk. We were not going anywhere that day!

Marina in Prince Rupert

Marina in Prince Rupert

Mistake Made

Deck mounted fill caps all look remarkably similar. Only by taking a close look at the writing can you tell the purpose of the fill hole. Often you identify it more by its position on the deck and what it is adjacent to than by what it says on the collar.

In this case, because we were moored stern in as opposed to bow in, the positions of the fuel and water fill holes were reversed to their usual orientation. I did not look closely. I just opened what I assumed was the water hole cap and began filling. It is easy to do without the fill caps clearly marked and without a double check procedure in place.

Lesson Learned

Putting fuel or water in the wrong fill hole is very easy to do. And the consequences are very serious and time consuming to fix.

Always double or triple check the fill hole identification when removing the cap and before actually filling. Consider having a standard boat procedure to have a second person aboard check every time you do a fill. It is that serious.

Take extra steps to have your fill caps clearly marked. I painted our water fill caps blue and our diesel fill caps yellow. You can buy replacement plastic fill caps in these same colours. Good idea.

Having at least two isolated fuel tanks is a good idea. When the mistake was made, we immediately switched to our second tank, maintaining our ability to run the engine and move the boat about.

Always carry a few jerry fuel cans in case you need to remove contaminated fluids for disposal. We had to borrow many jerry cans from folks along the dock.

Pumping out a fuel tank by hand is very difficult and time consuming. We were able to borrow a portable electric fuel pump, fitted with long hoses and wires with alligator clips, that we could connect to our batteries. What a difference it made. We now carry a similar kit for removal of fuel contaminated by water or algae.

It is not possible to remove all the water from a tank when the tank is still in place in the boat. Even with a second fuel rinse and pump out, a certain amount of water lingered. I can’t understate the water removal power of a Racor filter. Simply amazing! We have double Racors in parallel that allow us to witch back and forth. When one water bowl fills, we switch to the other and drain off the water in the first while the engine continues to run. We did this for a few days while sloshing about at sea and eventually removed all the water from the contaminated tank.

Be aware that water may sneak past your Racor filter and enter your secondary fuel filter adjacent to the engine. When I removed this filter, I was surprised to find it almost completely filled with water that had almost entered the engine. That would have created bigger problems.

It goes without saying that a good supply of spare primary and secondary fuel filters is a good idea. They are hard to find in remote places.


Luckily there was a large marine fuel depot nearby, with a huge dump tank for contaminated fuel. We made many wheelbarrow trips with jerry cans full of watery fuel. We then flushed the boat fuel tank and repeated the process. This was followed by Racor fuel filtering and several fuel filter replacements. Then we were off to Haiida Gwaii. A short while later, I colour-coded the filler caps with blue and yellow paint. So far we have had no repeats of this mistake. We learned!

Have a Story?

We have all made mistakes and learned valuable lessons the hard way. Do you have a story you want to share with BCA members, so we can learn from your experience? If so, please submit it for publication in this column, using the section headings ‘Submitted by’ through ‘Repairs’ or ‘Lesson Learned’. Thanks!

Send your story to with ‘OOPS!’ in the subject line.





  1. paul Carr says:

    A sorry tale indeed when there is water in the feul tank BUT there really is no need to worry as long as you are aware vit is there. Forward planning helps and all fuel tanks should have means to be drained from the lowest point. Water is one third heavier than diesel and does not readily mix. So a bottom drain regularly opened to inspect the contents at the bottom of the tank will save considerable expense from dealing with a contaminated high pressure pump. If a bottom drain does not exist then an opening in the top of the tank and the insertion of a copper tube to the lowest point will allow any rubbish including water to be pumped out at regular intervals as matter of winter layup practice. So often the maintenance of the fuel tank is ignored at considerable expense.

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