Powdered Block Filters
Powdered block filters are molded filters filled with densely packed powdered carbon. Water passes around the carbon filter, which limits its contact with water and therefore minimizes any taste concerns. Powdered block carbon absorbs many possible contaminants while the water passes through the filter. Because the powdered block carbon is itself not a completely solid block, bacteria can grow within the powdered carbon, making it important to change filters regularly.
Granular-Activated Filters
A granular-activated filter works in a similar manner as a powdered block filter, allowing the water or air to pass around the carbon. The large surface area of the granular carbon filter absorbs any contaminants while minimizing direct contact. Like powdered block filters, granular-activated filters need regular changing to minimize bacterial growth.
Solid Carbon Block Filters
A solid carbon block filter forces water through the carbon rather than around it, letting the water naturally filter through the carbon. Powdered carbon is fused with plastic polymers to create a solid block rather than a tightly packed set of granular or powdered carbon. This is the most effective way to remove contaminants, such as lead. However, this type of filter may affect the taste of the water for some people.
Silver
Because of the risk of bacterial growth, particularly in powdered and granular filters, some filters incorporate silver or other additives. Silver acts as a natural antimicrobial agent, limiting but not eliminating bacterial growth. Silver carbon mixtures last longer than plain carbon filters but ultimately require changing, after a certain period of time, to reduce the risk of bacterial contamination.