One of the most versatile pieces of outdoor gear to hit the marketplace in recent years is the stainless steel, single-wall water bottle. This rugged vessel is not only crack-proof and crush resistant, but it has a hidden advantage: It can be used to boil water to make it safe to drink.

But before you get excited and start fixing yourself a pot of campfire tea, there are a few things you should know.

First, the bottle needs to be of single-wall construction and made of stainless steel or another fire-friendly metal (titanium is one) with no paint or coatings. Don’t put an insulated or double-wall bottle in the fire. The heat won’t pass through properly, and the bottle will likely explode. Skip the aluminum bottles too, as the metal and the coatings can leach bad stuff into your water when heated.

A second line of consideration is functionality. It’s easier to retrieve noodles or rehydrated soup from and wide-mouth bottle, and they’re far easier to clean than their narrow-mouthed counterparts. The wide-mouths make a great survival kit container, too, as it’s easy to fill them with gear, and get the gear back out again.

Finally, how you boil water in a bottle is important. If you warp the bottle with too much heat, the lid won’t screw back on properly and the bottle loses its water transporting ability. The trick when boiling in these kinds of containers is to place the vessel beside the fire, not in it. Just snug the bottle up in the ashes on the side of the fire, wait for the big bubbles to start jumping, and then feed the fire so that the boil continues for 10 minutes. This will kill all the critters in the water that could sicken you, and keep the bottle cool enough to prevent warping.

Right now, I’m using an 18-ounce Klean Kanteen wide mouth for water boiling and cooking small meals, and a 27-ounce Klean Kanteen Classic for both boiling and water storage. It sure beats boiling a mud puddle with red-hot rocks.