The communities of bugs that live in fresh water supplies include giardiasis and cryptosporidium. The purpose of the water filter is not to kill the creatures, but to capture them inside the filter and prevent you from ingesting them. The effectiveness of the water filter is determined by what is known as the pore-size efficiency. This is the measurement of the size of the openings in the water filter. These measurements are microscopic.
The measurement used to describe the size of the filter's openings is called a micron. One micron is 1/1,000 of a millimeter. Any water filter with a micron size of one or less will remove parasitic eggs and larvae from the water as well as protozoa. To remove bacteria, the micron size must be less than 0.4 microns.
Regardless of the type of water filter, they all work in the same basic way. An intake hose is used to draw water into the filter. If you have a filter inside your water bottle, you'll fill the water bottle up first and place the filter inside. If you have a standalone filter, you can scoop water into a pail or put the intake hose directly into the water source.
Once inside the intake hose, the water is pressed through the filter, either manually, for a freestanding filter, or through suction, with a water bottle filter. The filter traps any microorganisms that may be living in the water -- and, like we said, it doesn't kill them. Once the debris is captured in the filter, clean water passes through and is ready for drinking. The area where the clean water exits the filter is called the filter outlet.