I am asking about the water quality in water balancing tanks, if there are studies regarding the relationship of the water tank types "plastic or metal tank", and the water quality..
plastic water tanks are FDA approved for drinking water, however only linear polyethylene will do, crosslinked PE can't be used with potable water (being around 50% more expensive you wouldn't want to anyway) I know that plastic water tanks release very little into the water (polyethylene reppels water rather strongly)
metal tanks must be lined before they can be used with water and therefore the metal the tank is made out of (unless it's stainless steel) is of little relevance, you have to consider the effect of the liner on the water instead, usually it's an epoxy spray-on coating and those must necesarily be FDA approved as well. I can't tell you much about linings though. maybe someone else can fill in there.