This article is intended to clarify the difference between my Urban Defender, a backwashing whole house water filter, and cheaper whole house carbon systems that do not backwash. Upflow filters cost less and are less effective. Backwash filters are more effective at contaminant removal and last longer. Finally, at the end of this article I’ll also address some misleading claims made by the manufacturers of upflow filters.
The backwash function on a whole house water filter cleans and redistributes the carbon media on a consistent basis at a specified flow rate for a specified length of time. The backwash also removes media fines to the drain. Proper back wash helps to provide consistent flow, increased contaminant removal and longer media life.
Upflow filters are less effective at contaminant removal
An upflow filter with no backwash results in inconsistent, typically inadequate flow to keep the media bed clean. An Upflow system is designed such that the water flows up through the media, theoretically eliminating the need for backwash while also providing a system that costs less.
Water Must Touch the Carbon in order to Remove the Contaminants
But by lifting the media during service there is necessarily less contact between the water and the media resulting in reduced performance. In other words, some water comes in contact with carbon particles while some water flows past the carbon without touching it. Contact time is critical to contaminant removal. This issue can be alleviated by manually backflushing an Upflow system on a periodic basis, but then that is the point of having an automated backwash cycle.
The upflow design will also result in media fines being lifted up and passing through top screen and into the home. With a backwash system, the fines are flushed to the drain. A sediment filter on both the inlet and outlet of the upflow filter can reduce fines entering the home but will likely clog and reduce water pressure.
From a more technical perspective the media inside of a backwashing whole house water filter will be compacted as the water flows down through the carbon. This provides greater contact between the water and the carbon. The water cannot pass through the filter without touching a large mass of carbon.
In an upflow system the water flows up through the media and the media is at least somewhat suspended in the water, depending on the flow rate. When the bed is fluidized in this way, water can easily pass around the carbon resulting in poor contact. When water is forced to pass through a compacted bed, the contact is far more intimate and effective.
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