If my water tanks had been made from this resin, perhaps my water wouldn't have tasted foul, despite fitting a new carbon filter. Although since the plumbing to and from the tanks consisted of standard transparent hose, I guess the water would have been tainted anyway. A good way to pollute your drinking water is to use transparent hose, to let some light in. Algae then inevitably grows and starts a food chain allowing other little beasties to reproduce. The hose solution is obvious though - use normal household plastic plumbing pipe. It's cheap, easily available, flexible to some extent, and doesn't impart unpleasant chemicals or flavours into the water. Why anyone would use hoses and jubilee clips is a curiosity.
I considered dumping the tanks, but I like the size of them:
They're as big as they could be fitting between a couple of bulkheads under the beds, and shaped to fit close to the hull. I measured them - 150 litres. This to me is a huge amount of water. Last summer I sailed alone from the Azores to the UK in 8 days. I had plenty of water on board, and made little effort to save water, but used just 25 litres. At that rate, with two of these tanks aboard, I could easily manage for 96 days. Perhaps if I caught rainwater from the coachroof, I could go on indefinitely. So even on an ocean crossing, I doubt I'd ever fill the tanks. It's just too much weight. But if I am going to spend a long time at anchor, or explore less habited areas, having the capacity to have so much water on board makes it no problem to do laundry and take showers.
When I bought some water tolerant epoxy to seal around the holes in my deck, I enquired whether there might be an epoxy that I could use to seal the insides of my tanks. There is, and it is called (amazingly!) AQUAPOX. Google that to find a supplier.
But how to paint the epoxy onto the inside of the tank? The stuff is quite expensive, so I wanted to do a proper job, and also, I really did want to drink water without styrene in it.
The tanks were gel coated on the inside. The gel coat would need removing first, as the epoxy couldn't stick to that very well at all. The only way to do that was to cut the tanks open. I had to do this anyway to work on them, as they are bigger than the doors.
So, I cut them in half with a grinder using a thin metal-cutting blade. I then ground off all the gel coat, and painted the insides with Aquapox. I took them back into the cabins for reassembly. I held the halves together with tape, and stuck strips of glass at various places to hold the halves in the right position. Then I took the tape off, and wrapped the joins with several layers of glass tape and epoxy (epoxy sticks better to old polyester resin than polyester resin does). With a bit of stretching and the use of a small mirror, I managed to fill some gaps in the joined are with some more Aquapox.
The Aquapox needs 8 hours at 40 degrees to cure. I managed that by inverting the tanks and covering them with a duvet, and using a hot air gun with a thermostat propped up, blowing warm air inside.
The tanks don't look pretty on the outside, but there was no point painting them, so I reinstalled them, gave them a quick rinse and started using them.
I now have water that tastes as it ought to, and no longer have to apologise to guests for the funny tasting tea.
Still, that was a lot of work which produced no visible signs of improvement! It helps to write it down!