Not all water filter systems are the same. All systems work on the principle of directing in flow fluid so that it passes through a membrane or mesh which in turns extracts impurities from it. The goal is to be able to get rid of the impurities that are harmful to your health. A byproduct is that the liquid then becomes more attractive to consume because of its visual clarity, pure taste and fresh smell.
Simple set ups will only get rid of impurities of larger size, twigs and leaves for example, which might cause blockages in the supply line or fester in a holding tank tank if it is to be stored. The membrane size will determine which and how many of the contaminants are removed. It stands to reason that the smaller the filter the greater the number of contaminants that can be eliminated.
It is not unusual to see a system that has a large mesh membrane that filters the medium to be stored like, say, a rain collection system. This fluid then maybe further filtered at the kitchen sink for cooking and drinking purposes. A drinking supply in most cases does require some fine filtering to enhance taste and smell, even if it has no dangerous content and comes from a municipal supply.
Fine and very fine meshes or hyper filters require the fluid to be pushed through them with some force. If this does not happen then the outflow side of the system may produce only a few drops or slow dribble at best.
This is often achieved by employing a reverse osmosis unit. These can raise the pressure of the fluid on the inflow side to achieve an acceptable outflow after passing through the fine membrane. These systems can also manage to dispose of the contaminants on the in flow side of the system thereby increasing the system’s efficiency.
This technique of purification was originally devised to extract fresh H2O from the sea by filtering out the harmful salts. It has gone on to be the chosen system for use in some large municipal desalination plants. It is also and is often used by the military to provide clean liquid in hostile and unsanitary environments.
Thankfully smaller domestic scaled reverse osmosis water filter systems are available at reasonable cost. They are slightly more bulky the familiar standard under sink filter but for not much more can provide a better cleaner product.