Stainless steel, also known as inox steel, will not readily corrode, rust or stain from water contact and moisture.
The strength and durability of stainless steel makes it a desirable, yet it is also significantly more expensive option. Due to its expense it is normally used in products where both the strength of steel and corrosion resistance are required. So we see stainless steel used in products like kitchen sinks, cooking vats or rainwater tanks.
It should be understood that “stainless” steel is not entirely stainless. Pitting is a form of corrosion that can lead to small “pits” or holes. It is therefore important to regularly clean stainless steel products and equipment with fresh water. If you notice rust spots occurring on your stainless steel product, then remove the rust spots and clean as soon as possible to prevent irreversible damage.
Also important is how a stainless steel sheets for tank have been joined together. An investigation by the Public and Environment Health Services in Tasmania found water in some stainless steel tanks containing harmful levels of lead, because lead was used to solder the stainless steel sheets together. So there is also the added risk of safety to your drinking water, that is, if your steel tank does not have a food-grade inner poly lining.
Depending upon the grade of stainless steel used in your rainwater tanks, some warranties will not cover marine environments. You will generally want your water tank to be a minimum grade of 304 Stainless Steel, which is the same as your kitchen sink. For marine environments it is recommended that you obtain 316 Stainless Steel.