Sediment Cartridges		These cartridges remove particulate matter from your water, and should be used as the first stage of any filtration system. They both clarify your water and protect down-stream filters and plumbing from premature failure.
Carbon Cartridges		Activated carbon does a remarkable job of improving the taste and odor of water. These cartridges should ideally be used as the second stage in a filter system, protected by a sediment filter ahead of them. The pictured model is one of many available, and is a similar equivalent used in either a single or double filter system used by RV manufacturers, such as Watts, Premier,  FloPur and WaterPur for a whole RV filter.  Note the comments on the modified carbon block combination cartridges mentioned just below.
Combination Cartridges		Combination cartridges combine both sediment removal and taste-and-odor improvement in a single cartridge. Ideal used with a single external canister, they provide a good compromise where space does not permit two canisters.  These are modified carbon blocks and make an excellent replacement cartridge for existing filter systems used by a number of RV manufacturers and water filter brands.
Specialty Cartridges		A variety are offered and depending on flow rate, these filters may be good in multiple outside systems or in the kitchen at point of use. This style of cartridge is used quite often by Hydrolife and Shurflo filter systems.  It uses granular carbon and a substantial amount of KDF, a zinc and copper alloy that adds a number of benefits to the cartridge.