I'm pretty sure it doesn't matter, but someone gave me this big spiel about making sure it was drinking water safe so it didn't have chemicals and crud in it when I first got all my materials, so I got one anyway.
If you're looking for them, they're carried in most stores like K-Mart, Walmart, Home Depot, Lowes, any camper/rv supply store, etc. It'll say "Drinking Water Safe" on the label and they typically are a different color than the normal ones. Mine's white.