Ok, time for a lecture. Cast iron is made of iron (can I say anything more obvious?
). When iron comes into contact with oxygen, it will combine with that oxygen and create iron-oxide (rust). This is the most stable form for iron. As a point of fact, iron ore is actually iron oxide and must be treated to remove the oxides giving us the iron for all ferric products. Where the water comes in is that water is a great electrolyte. That is, it acts as a conduit for electrical energy. Place a little water on iron and it allows the conbination of the oxygen from the air and the cast iron, resulting in rust.
The seasoning we create on all surfaces of cast iron act as a hermetic seal against air and water coming into contact with the base metal. And since it is carbon based (very slippery stuff, that carbon), it makes the metal stick resistant as well. It also protects the metal from contact with acidic an alkali ingredients, i.e. tomao sauce, baking soda. Acids and alkalies both make great electrolytes, allowing the transfer of electrons through the material, again causing corrosion.
Ever wonder why tomato sauce cooked in cast iron tastes like iron? It's because the acidic tomato sauce leaches ferric ions from the bas metal. If a cast iron pan is seasoned correctly, you can cook anything in it without fear of metalic flavors in you food, because you've protected the pan from contact with the food through the pan seasoning.
I have a problem with using cast iron grilling pans in the house. When heated sufficiently to give meats a great sear, and hence, great flavor, they smoke up the house like crazy. I only use my c.i. gill pans when I'm cooking outdoors, say on a campfire, where the resultant smoke does not create problems, and in fact, helps flavor the food.
There. The lecture is over. Recess time. Go play, kids.
Seeeeeeeeya; Goodweed of the North