Know your filters and what they do
Filters come in various types and sizes and do different things.
No single filter will take care of all your water treatment needs. A filter is basically a screen that catches particles in water and still lets the water run through. Filters with smaller screen or micron sizes trap more debris, but the small size restricts water flow, and the filter clogs sooner and has to be changed more often. The amount of particulate matter caught in your system; roof, gutters, and tank also determines how often you need to change the filters. Filters can harbor bacterial growth, so it is important to maintain and change them regularly.
According to Patricia Macomber with the College of Tropical Agriculture at the University of Hawai'i at Manoa, once a month is the standard for sediment filters, but that varies depending on the size of the filter and your system’s conditions.
Most filter holes are too large to keep microorganisms from passing through with the water, so you are not safe from pathogens just because you have a filter. You should understand exactly what you want your filter to do, then purchase one that does it.
Water pressure can force larger particles through pore (hole) sizes that would normally be too small. As pressure builds behind a dirty filter, more particles will get pushed through the filter. Therefore, pore size and filter function are not absolute; as the filter ages, the material in it can stretch, wear down, or tear. This is another reason to change filters on a regular basis.
We often hear the string and paper filters are considered 'forever' filters because they never fill up or influence water pressure.