You can only strain so many pots of noodles before your colander is crammed full of noodles. Similarly, filters clog and need to be replaced. If you have a filter that needs frequent replacement it could become very costly. Also, you may not have access to the replacement elements during an emergency so filters that need frequent replacement of parts will become ineffective quickly. Another negative aspect of filters is that sometimes you can filter faster than the filtering element can clean.
Filters work by pumping a handle manually.
Sometimes you have to pump very slowly to catch all the particulates in the water. Impatient, forceful pumping can shove particles through the filter and into your drinking water. Purifiers have equally significant downfalls. Because the active ingredient for treating water in a purifier is iodine, some people should not drink water from a purifier. It is recommended that pregnant women or people with thyroid problems do not drink from iodine-treated water.