hi
there is a 40 litre stainless steal tank up under the V-birth which installed when the boat was built in 1984 and it is currently plumbed to the galley tap. I have not been game to drink the water from there as I don't know what lurks inside the tank 
If I was to have the tank steam cleaned and used new pipes would I be able to use it for drinking water? And also what treatments if any would I be best to use. Or am I better throwing the tank away, it seems a shame as it so snugly fits in under the v birth
I imagine there will be some muck in it after all those years, I would take it out and clean it by steam cleaning or even by boiling it with a mixture of water and caustic soda. Boil it for at least an hour then drain and rinse, rinse it again, then to be on the safe side pour some vinegar into it and swish around to neutralise any remaining caustic soda, rinse a couple more times and flush and clean the pipes before installing again. Fill with clean water and go and make a cuppa.
Replace the tank would be the last thing to consider . Believe stainless tank is priceless. Don't bother to remove it,
install inspection opening, you can poke your hand through. Polish stainless with Gumtion ( used to be Whitte Lily ).
Rinse and fill up with a few litres of water with a few Miltons tablets ( any supermarket, even safe for babys utensils ).
Leave a couple of days sailing, sure replace lines.
5 ltr or 10 ltr cask water is the best at Coles or woolies....save the tank water for shower and dishes !
We use the 10 litre water bottles with tap. They are the ONLY time I would buy bottled water.
For drinking water I have a 20 litre distilled water container and tap bought from the local dentist, empty, $5.
please be careful what you put in the tank, not only for consumption but for damage to metals and piping.
the residue left behind is most likely of a brown / sediment stain and totally harmless. if its thick and sludgy, a little chlorine or iodine liquid to stop any germs you might be concerned about and a wet vac or clean rag to soak it up, assuming there is access. or install a 2 stage filter from reece plumbing supplies or the like. easy to do.
if its a stainless tank and you have a leak, throw a good quality flexible container in a hatch in the tank. spread it out and fill her up. if flavour with the new tank is a problem then install a .5 micron filter in the system and itll be just like bottled water.
Not sure if domestic filtration is any good on boat. Simply they need pressure to work.
Microfiltration 5 to 0.05 micron, is very basic anyway,moderate effectiveness.
Clean tank and town water, never had any problem.
yeah they need pressure thats why pumps are around. works perfectly with any pump even at lower pressures but the flow rate reflects this. we had 1 outlet (filtered) for drinking / cooking, another for washing etc in the galley.
All odour from flexible tanks was removed.
If the filter removes "odour" from bladder tanks it suggests you get more than odour in the water from them ie particles which in some way have to be toxic.
So filtering water sounds like a good idea but using bladder tanks sounds like not a good idea.
