In a previous post, I talked about what gives water its flavor. But what do you do if you do not like the flavor of your water? Or what if you think metal is sloughing off old pipes into your water? I personally do not think it is worth it to buy bottled water. I have great faith in the public water supply because tap water is more rigorously regulated than bottled water. Tap water falls under EPA jurisdiction which has higher water cleanliness standards than the FDA has for bottled water.
But for some reason our apartment water has been smelling like a swimming pool lately. I’m glad it smells and tastes like chlorine instead of lead, but still, it is unappetizing. So we hooked up one of those water filters that you can attach to your sink faucet. It works like a dream. Now our water smells and tastes “normal”.
In the process of picking a filter I looked into how home water filters for faucets work. Most filters have activated carbon inside of them and some have ion-exchange resin.
What is activated carbon?
Activated carbon is also called activated charcoal. It comes from materials such as coconut husks, wood, and nut shells that have been burned down in specific conditions. The ashes undergo more processing based on their end purpose. The end result is a highly porous material that can absorb odors, colors, and other organic compounds. Molecules get “stuck” in the bonding sites of the activated carbon. When all the bonding sites are full, the filter needs to be replaced. Side note: activated carbon can be cleaned and reactivated but it is a practice only done in industry.
What is ion-exchange resin?
Ion exchange resin does exactly what its name says: it exchanges ions. One charged atom swaps places with another. For water purification, harmful ions such as copper, lead, and cadmium switch places with ions such as sodium and potassium. The resin is the support structure. It is made from an insoluble polymer, normally in the form of little amber or white beads.
Anything else?
Some filters also have a layer of minerals for the water to filter through. This layer gives the water a specific flavor. Pretty cool huh? I’m amazed all of that can fit into a little filter and work so well. Of course, not all water filters are made with the same filtering layers. Check the filter’s performance data sheet for specifics.
Photo 1: Zsuzsanna Kilian
Photo 2: RaveDave
Photo 3: Bugman
A Dash of Science 
So what are the tradeoffs with using each type of filter? Is one more expensive than the other?
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Many faucet filters have both filtering materials in them since the materials target different contaminants. The activated carbon targets organic material (odors, sediment, etc) and chlorine. The ion-exchange resin targets minerals. If you did get a filter with only one material, less would be filtered out. Since tap water is already fairly clean, the biggest difference would be in taste.
I am not sure which type of filtering material is more expensive. There are several other factors that contribute to the price of a faucet water filter.
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