Countertop systems are suitable for those persons that want an easy to fit water filters system that is economical to purchase and is portable.
The diverters attach to the thread on the end of the spout or tap where the aerator usually is, to the right is a photo of the aerator removed from the tap so you can see what they look like, this one has male threads but there are also female
When the little handle is in it's normal position the water goes into the sink as normal, it is only when this handle is turned does water get diverted through the filter system.
The image on the left is with the water going through the filter and the image on the right is with the filter system off and the water goes into the sink as normal.
Here is a picture of the premium system installed with water running through the filter system.