I have a countertop water filtration unit that I use tirelessly, for both drinking and cooking water. With normal use, one filter should last about a year, but I just changed mine after eight months since the water flow had slowed to a trickle.
The reason? Take a look at the photo; that's the new, pristine filter on the left next to the used filter with its collected detritus.
Below, copied from the filter's replacement manual, are some of the contaminants the filter reduces (I wonder what isn't caught!). And, by the way, I live in a municipality with a water supply that is generally considered to be excellent. Ever wonder where all that pesticide run-off goes?
Also, it is sobering to think about people who walk hours to fill a jug or two of potable water.
Contaminants possibly contained in the darkened filter:
Nominal Particulate Reduction (Class 1)
PCBs (polychlorinated biphenyls)
Taste & Odors
VOCs (volatile organic compounds)