In general, stay away from plastic, aluminum, teflon, etc. in your cookware. Anything heated should definitely not go into those things.
Stick with glass, stainless steel, cast iron (not recommended for water unless there is a coating, usually ceramic), ceramic.
If you save glass containers from food items you buy, check those lids. Some of them have a painted surface that scratches off. Sometimes rust comes out. I would be wary of those.
Checking steel vs. aluminum: steel is an alloy that will respond to a magnet; aluminum won't.
Anything teflon/nonstick will, obviously, have an oddly smooth surface, water will bead on it, it may look flecked, etc.
Anodized aluminum might be OK, but it's safer to stay away from it. Regular aluminum cookware (dull silver surface usually) will react with and leach into your food.
It's the surface that comes into contact with food that matters most. Many pots & pans have an aluminum layer, because it conducts heat, but it should be sandwiched in the middle of the layers composing the pot/pan.