Solid Carbon Block Drinking Water Systems have combined the incredible adsorption capability of carbon, with the ability of a solid block of material to selectively strain out particles from water that is forced through it. The density of the carbon block determines how finely the water is cleaned. The better brands of this type of filter have a three-part filter and are designed to prevent any possibility of "bypass" due to high water pressure. 

The following list of features are what combine to create the type of filter that will remove the widest range of possible contaminants in the drinking water: 

Mechanical Straining: 

The block of carbon mechanically strains out dirt, sediment, rust, algae, bacteria, microscopic worms, cryptosporidium and asbestos. This is all accomplished by water pressure so no electricity is required -- such a filter even works on a simple hand pump in emergencies! 
The compacted solid carbon block filter is designed to mechanically filter particles down to sub micron size. By micro- straining the water, the consumer is assured that only the cleanest, clearest water is delivered to the point-of-use. 

Chemical Bonding: 

Activated carbon bonds to thousands of chemicals. In fact, carbon will bond to most chemicals known! When water is forced through the solid carbon block, it is forced to slow down and increase the contact time with the carbon, allowing the carbon bonding to take place to remove the chemical pollutants like toxins, pesticides, THM's, chlorine, bad tastes, odors, etc. 
Heavy metals like lead do not bond to the carbon, but are strained out by the pore size of the block. Basically, it's like trying to put a basketball through a hole the size of a ping pong ball. 

Prevention Of Bacterial Growth:

Because of the density of the solid carbon block, there is no room for bacteria to grow so this type of filter does not become an incubator for them.