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.
Backwashing carbon filters are more effective at contaminant removal
Backwashing provides the needed time and flow to sort the carbon on a periodic basis. In other words, the backwash cycle is deliberately designed to first lift, shuffle, and then resettle the carbon. This can be weekly or even monthly is usually adequate. The backwash cycle forces the water to establish new pathways through the media allowing for an even flow, exposing the water to fresh carbon. This results in more contact and thus, more contaminant removal.
Without periodic backwash, the water will find paths of least resistance through the media bed and continually follow through those paths. We call this “channeling.” This channeling exhausts the carbon in that path at an accelerated rate. This diagram shows how the incoming water is forced through a solid bed of media:
An upflow filter is in this constant state of backwash when water is turned on in the home. It is possible for individual streams of water to totally pass individual particles of media thus avoiding removal of contaminants.
Backwashing filters have greater contaminant removal
A backwashing whole house water filter will provide you with greater contaminant removal and a longer media life than its less expensive upflow alternative. In water treatment the old adage ‘You get what you pay for’ is always true. If I felt good about upflow carbon systems I would be selling one.
You have to be alert when you review the claims made by water filter manufactuers. Elsewhere in this blog I have discussed the problems associated with the NSF 42certification. Most manufacturers will make a statement about the removal of chlorine.
However when you look at your local water report you will also see listed chemical groups known as the haloacetic acids and trihalomethanes. These are known carcinogens that are produced when chlorine or chloramine comes in contact with organic material in water. These compounds are present at higher levels when your water source is surface water such as a lake or river.
Upflow systems generally have less carbon than downflow systems. It is the carbon in the filter that removes the haloacetic acids and trihalomethanes. A whole house water filter that uses the downflow technology is more effective at removing these carcinogens.
These systems may also include KDF, which is a media I like very much. The KDF converts chlorine to chloride thus eliminating that contaminant.
The carbon will be subject to channeling shortly after installation. The really deceptive part is that the small amount of carbon will be quickly exhausted – by becoming saturated with contaminants. It’s simply not enough carbon to last long. The KDF will continue to convert chlorine so you won’t detect any change to water quality. What this means for you is that you’ll be bathing in the carcinogenic byproducts of chlorine, the trihalomethanes and haloacetic acids, while you think you’re bathing in treated water. These same salesmen may also have led you to believe that the water is safe to drink, so you’ll be drinking carcinogens. You’re better off to save your money and buy a shower filter which does exactly the same thing.
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