Choosing the right carbon water filter for your application can be a daunting task.  What are the differences between various types?  Does it really matter if I’ve got the right microns?

There are three types of carbon filters: carbon-wrapped/impregnated, granulated carbon and carbon block. All three will improve taste and remove chlorine, but they do have important differences in how well they do it and what else they do.

These are generally used in drinking water systems and sometimes as part of a watermaker fresh water flush system (to remove chlorine if you use bleach in your water tanks).

Carbon wrapped filter Carbon wrapped or impregnated. These are generally the cheapest of the carbon filters. They are also the type of carbon filter that is easiest to find.  If you are simply seeking to improve the taste of your water, most will work fine.

However, it’s important to note that they reduce the chlorine in the water, they do not totally eliminate it. Do not use these in any application — such as the freshwater flush system of a watermaker — where total removal of chlorine is needed.  Any amount of chlorine will damage a watermaker membrane.

Granulated charcoal filter Granulated Charcoal. The big thing to know about granulated charcoal filters is that they do little to filter sediment from the water.Further, they do not come in fine enough filtering to remove giardia.

They are easy to identify as they have a solid plastic outer casing.Granulated charcoal filters are reasonably good at removing chlorine, volatile organic compunds, pesticides and many other man-made substances. They typically come in 2 to 20 micron filtration levels.The best use for granulated charcoal filters is simply to remove bad taste from drinking water.  

Like the charcoal wrapped filters, they do not sufficiently remove chlorine to use on a freshwater flush system with a watermaker if you use bleach in your tanks (or if you alternate watermaker water with city water that could contain chlorine).

Carbon block filters.Carbon block filters can remove small quantities of heavy metals, but they can’t cope with high concentrations and shouldn’t be relied upon for that. Only the finest 0.5 micron carbon block filters will remove giardia and cryptosporidium, both of which can cause severe diarrhea.  

A carbon block filter’s effectiveness at removing sediment is dependent upon the micron rating of the filter, although water with visible dirt and sediment will quickly foul the highest quality carbon block filters.

Carbon block filters can be made from any of several materials; coconut shell carbon is the best, but also costs a little more.  While sediment-only filters can simply be changed when the flow rate has noticeably lessened, carbon filters will lose their full effectiveness long before taste is affected.  If you are using a very fine carbon block filter, be sure to change it according to the manufacturer’s directions in order to get the full benefit.