Fiberglass Fuel Tank Conversion Back to Water Tank

The operative word is or.

Like dead or alive.

If alive, easy to become dead.

Once dead, difficult to become alive, again.

Q,
Invest in a new tank, bladder or other means where you will not be storing potable water near or in a container that stored diesel for 7 years. Here's a statement from the web: International Agency for Research on Cancer (IARC): Group 2B, Possibly carcinogenic to humans (Marine diesel fuel) or Group 3, Not classifiable as to carcinogenicity to humans [Distillate (light) diesel fuels]

More info: Potential Symptoms: Irritation of eyes, skin, respiratory tract; dizziness, headache, nausea; chemical pneumonitis (from aspiration of liquid); dry, red skin; irritant contact dermatitis; eye redness, pain

Health Effects: Irritation-Eyes---Mild (HE-16); Kidney damage (HE3), Potential lung damage (HE-10); Suspected carcinogen (Marine diesel fuel) (HE2)

Affected Organs: Eyes, skin, kidneys

Not that trace amounts would cause any of this, but why take a chance with yourself, family and /or friends.

I wouldn't do it, period.

It would not matter what was done, how many reassurances, who did it, or anything else, there is no way I could ever knowingly drink or even bathe in water that I knew was from a container which once held fuel. I would pursue any different avenue. Do you have another water tank currently of any type? I'd give up anything else. I'd even put a bladder on deck or where a locker is now or under the bed or somewhere.

Aluminum is not porous, and a sewage tank that was sterilized properly, knows no difference as long as you change all the lines and everythi. Fiberglass that held fuel is a totally different story and I would never trust it for freshwater usage......

Aside from that, I wouldn't drink water that came out of ANY boat's freshwater tank......Bathe in it yes, drink it never.

Well, we only drink bottled water so that part is easy. But washing dishes, cooking, and then bathing. You're right on two differences, aluminum versus fiberglass and black water versus fuel. Both are significant. Although I still wouldn't do the black water to fresh water routine, there are actually means to sterilize the aluminum tank in that case. There are none I would trust to treat fiberglass or to remove the fuel impact.

Taking shortcuts that potentially impact your health, your family's health and your friends' health just are not something I'd ever consider.

The rivers you mentioned are the ones that every city along them gets their water from. Obviously they have huge treatment centers and personally I wouldn't drink it, but I'd use my watermaker for everything else.

Yeah, you can use your watermaker on inland rivers if they're not polluted with oil or whathaveyou. You have to run the high pressure very low, like 100 PSI with freshwater. Get the watermaker going and just keep the pressure just high enough to make it's rated output.....if its 50 gph, keep it at 50gph. The output will keep rising as it cleans out the membranes the first couple of times you use it, so you'll have to keep an eye on the high pressure for a while......but if you set it to around 100psi you should be ok.

I'd be more concerned about having enough fuel in those places than water.....Diesel stops that can accomodate a large boat are few and far between.

Why would you have to wash the boat off in rivers anyways? There's no salt or anything to rinse off......maybe a little soap and water to wash the soot off the transom. Are you never going to stay in marina's where you can fill up the freshwater tank?

If you already have some kind of grey water tank, a circular conversion fuel->grey, grey->white might make some sense.
But honestly, fuel-soaked fiberglass won't make a good clean water tank.

Well depends if you are running a military or navy... don't matter done all the time. The crew or troops gets sick just get rid of them and get new... . Actually, most militaries used fuel tanks for portable water too... with not much effort other than draining. It may not be very good or lead to a long life or someone will get sick every once in awhile... no one cares. Much of the time these are fabric reinforced rubber tanks... worse than your fiberglass situation.

Its like drinking out of some stock pond or watering hole in some third world country... done all the time...

I have drank out of both... not pleasant but if you are thirsty enough you will. Never got sick but some have and got unpleasant cases of parasites too. But then some worms probably long ago eat the better parts of my brain anyway...

Seriously, the water can be made potable but will always have an unpleasant taste.

Dual use of fuel tanks

The US Army did exactly that during the first Iraq war. Fuel trucks for kerosin and diesel were transporting potable water, when not needed for fuel supply. And these trucks were only rudimentarily cleaned, if at all. But the Army has learned her lesson the bad way. Hundreds of soldiers became seriously ill because of carbon hydrogen poisoning. A lot of veterans are still suffering from Nerve Diseases and other very bad things. To my knowledge, not only a few died because of this procedure.

Never ever use tanks both for fuel of any kind, like Petrol, Diesel or Kerosin, also for potable water, regardless of tank material (GRP, metal or rubber). As rule of thumb, 1 liter of fuel / oil poisons 1.000.000 liter of water. Even if you dont drink it, your are still harming the enviroment.

If you have to use a fuel tank for some odd reason as a ballast tank, when empty of fuel, or visa versa, a ballast tank as a range extender, place a bladder tank into the permanent tank. When the outer fluid is used up, you can fill up the bladder and never mix two fluids, which do not belong together.