The Whole House Unit system is mounted where the water enters the home, and a plumber is recommended for installation. This unit filters all the water in the home: drinking, bathing, brushing teeth, washing clothes, etc. 
 
If your home is older (lead pipes) or you live in a high contamination area, consider a combination of Whole House Unit + Under Counter Unit. The Whole House filters water entering the house, and the Under Counter filters water prior to drinking or cooking thus further reducing harmful contaminants that may be present in the house plumbing infrastructure. We've bundled these for additional savings.