NSF International certifies water filters — this certification ensures that the filters do their job, and do not re-contaminate the water with bacteria. Most filter manufactures will advertise that their filters are NSF certified. However, many commonly available filters will let quite a few contaminants through. For example, granular filters do not utilize the chemical adsorption process, allowing several contaminants to pass through. Likewise, rapid water filters do not give the water adequate contact time with the filter media, limiting the number of contaminants that may be removed. For example, in-fridge or faucet-mount filters may not filter VOCs and chlorination by-products like Trihalomethanes (THMs). Generally, slow filtration tends to be best. Drip filters will remove a wider range chemicals, pesticides and MTBE (a gasoline additive).
In my home, I use a Big Berkey drip filter, (pictured above). I like drip filters because they provide great quality filtration, and they are inexpensive to use, because they don’t need to be replaced. You can clean them with a stiff brush if they become dirty with sediment. To use a drip filter, you pour tap water in the top, and the water slowly drips through the filter to the bottom compartment. The process takes a couple of hours.
My Berkey filter contains two Black berkey filters. You can get them with four filters this cuts the time for filtering
You can find out more about them here WaterFilterbyBerkey.com