Many different types of portable water purifiers exist, but one of the most popular is the kind that uses a ceramic filter which is enclosed in a cartridge. This kind of filter will remove even extremely small particles.
Activated charcoal is also a popular choice for purifying water in a portable system. These are capable of removing protozoa, bacteria and other extremely small contaminants, but not viruses. The only systems that can destroy viruses are those that use chemicals or ultraviolet light.
An older version of portable water filtering systems are the ones that have polymer filters. These are not very popular today, since they tend to leave a taste to the water, and there were even some Arctos Portable Air Cooler reports that residual iodine was left in the drinking water, and this is very unhealthy. Portable water filtering systems were developed for the armed forces to assure survival in remote locations. but now they have been developed for general use.
One of the problems with portable water filters is that they may encourage the very contaminants they remove. These contaminants, such as bacterium and fungus may stay in the filter portion and start to grow there. To eliminate this problem, many manufacturers have to add a feature that creates a barrier to these particles. Nanoparticles make of bonded silver are added, and this prevents the growth of these pathogens.