I’ve gotten a number of comments recently regarding my water bottle. It’s one of those fancy Bobble bottles, where the carbon filter is attached to the cap so you can theoretically have clean water anywhere you can take the bottle. It’s a unique and nifty invention in a market that’s suddenly obsessed with more than just “good” water.
Sometimes people look at my water bottle and ask, “does it really work?” Hmm…well, I’ve always hoped so. I realized that I’ve been blindly lured in to the filtered water industry by the successful marketing strategies of companies like Brita, PUR, and Bobble. Darn.
So, do these filters actually do anything? Well, these common commercial filters are made out of “activated carbon,” which is basically a form of charcoal with lots of holes in it. The more holes in something, the bigger the surface area, and the bigger something’s surface area, the more space there is for chemistry stuff to happen. Think about it like a dresser. If it was just a block of wood, I suppose you could set stuff on the top surface. But, your clothes would quickly become an unsightly pile of socks and sweaters. If you added more surfaces, like shelves or drawers, you could fit a lot more clothes in it, and use the space more effectively. Crushing up a material that contains carbon, like coconut shells, wood or charcoal, bursting it with oxygen, and baking it is the general process for making activated carbon. Forcing the oxygen into the carbon, then adding excessive heat to force the oxygen back out creates lots of holes between the carbon atoms where the oxygens left, i.e., lots of tiny surfaces are made on which chemistry stuff can happen. This is a bit different than making charcoal for your grill, which is treated with chemicals and not oxidized (A closer look at the process: here.).
That’s all fine and dandy, but what’s the point of running water through a hunk of porous carbon? Since the carbon has lots and lots of tiny nooks and crannies, it can absorb molecules that are floating around in the water. Carbon filters can absorb things like chlorine, pesticide residues, sulfur compounds (things that smell like rotten eggs) and compounds called THMs (THMs stands for trihalomethanes, which are things like refrigerants and chloroform that I, personally, would rather not be drinking.) There are many chemicals that aren’t attracted to the carbon, like metals, but organic compounds (molecules containing carbon) are generally absorbed.
Activated carbon is like a series a of complicated roadways that get narrower and narrower until the cars get lodged in an alleyway, and they’ve gone down so many roads, they couldn’t make it back to the highway even if they wanted to. Eventually, the cars will get so backed up that the roads can’t hold anymore, and the cars end up on the highway without ever getting trapped in the maze. This is why you have to replace carbon filters. So many chemicals get stuck in the filter that it just can’t hold anymore, and they end up back in your drinking water (the same way sweaters end up on your floor if your dresser gets too full).
I know my carbon filter can’t remove everything from my water, but at least I know it’s not removing nothing from my water. Although, since I’ve been assuming the marketing for carbon filters is accurate, I guess they could have been getting away with a filter that doesn’t do anything. Yay, research!
Sources: Chemistry in Context, Applying Chemistry to Society (A Project of the American Chemical Society, Fifth Edition)
Activated carbon. (2006). In McGraw-Hill Concise Encyclopedia of Science and Technology. Retrieved from http://www.credoreference.com/entry/conscitech/activated_carbon