There are those who say that the nickel in stainless steel can cause cancer. That sounds nutty, and it probably is, but more than one doctor has recommended not to cook in stainless steel pots or pans, or use stainless utensils.

Personally, I wouldn't worry about plastic bottles. More than likely the water you drink has passed through a few plastic pipes on it's way to your faucet, so avoiding plastic bottles seems rather superfluous. If you want the cleanest and safest, use glass. But, once again, the bottle may be cleaner than the water you are putting into it.