You may recall these pictures of one of the tanks. They are un the bottom of the hull accessible through a 1m square hatch in the lower deck floor. Then the hole to get into the tank is quite tight.
The problem is that I would not trust water out of these tanks. Not to drink anyway. So I need to get them sorted. It seems that while we can put a man on the moon and visit the deepest parts of the oceans there is no simple way to do this job. I would have thought (but turns out I am wrong) that there would be some paint that would be able to go over the existing covering which is approved by WRAS (DWI) for potable water. But no. That would be too simple.
There are therefore 2 main options. The first is an epoxy covering. Either spray on or paint on. But it will only work on metal. The insides of the tanks would need to be sand blasted. That would be like trying to sand blast the inside of a telephone box on its side while inside it and the box at the bottom of a coal mine. Nightmare. I have looked into this and it is doable but will be a horrific job.
The second approach would be to use a lining. But again this is complicated as there are baffles in the tank (to stop the water sloshing about too badly). These make the job difficult.
I think the solution will be to remove the baffles to make the tanks able to be lined. I will survey them when I am next down. I suspect I will line two tanks for drinking water and then paint the others with some other covering that is chemically resistant for the waste tanks.
The final alternative would be to fit new tanks but they would need to be fitted on one of the decks and there are advantages to having that weight in the hull and not higher up as it makes the ship less likely to lean.