Why are there spots or pitting on the inside of my stainless steel pan?

Ordinary water and food contain salts and acids which can sometimes cause minor markings on the stainless steel surface, particularly on brand new pans. This is common when cooking starchy potatoes or pasta, but the most common cause is adding salt to cold water. The salt fails to dissolve in the cold water and sinks onto the base of the pan where the sodium reacts with the nickel. Always add the salt to the water once it is boiling.