Water Filtration Basics

Pure Water - A Pipe Dream?
Pure water contains only one chemical compound: H₂O. It is rare to find absolutely pure water, though, as water easily picks up and carries other stuff, and most of it is undesirable.  It's the undesirable stuff that has gotten into water that you are trying to remove by filtration. 

Types of Contaminants in Water
There is a wide range of contaminants that might be found in water, but we can break them down into two main groups: those that affect only our aesthetic senses (sight, smell, taste), and those that affect our health. Most folks want to address both groups of contaminants when choosing a filtration system for their RV.  Let's look at each group a little more closely.

     It Tastes Bad, It Smells Bad and It Looks Revolting!
Ever had that reaction when you drew a glass of water? Then you've experienced water with some contaminants that affect your senses. Let's break this group down into two sub-groups: those affecting the appearance of water and those affecting the smell and taste. Now let's look at each of these sub-groups a little closer.

     If It Looks Bad, It's Probably Got Sediment
Water with noticeable haze or murkiness is carrying particulate matter that is referred to as sediment. However, large particles settle out of water pretty fast, so what water is carrying is very small particles. If there are only a few, you may not even notice them, but if there are many, you have hazy or murky water. In addition to the noticeable affect on water clarity, sediment can also create problems by plugging up other filters you may be using, causing them to fail prematurely.  The brown filter cartridge in this photo was in use for only 3 weeks, and is shown next to a new one!

    How Small is "Small"?    "Microns" (one thousandth of a millimeter) are used to measure the size of particles in water. Filters, too, are rated in microns, and the smaller the micron size of the filter element, the smaller the particle it will remove. A 20-micron filter will remove particles 20 microns or larger in diameter, while a 5-micron filter will remove sediment  5 microns or bigger.  These micron ratings are nominal, or approximate.  Sediment filters work by straining out the sediment and holding it. As you can imagine, as the filter collects sediment, it gradually plugs up and reduces the water flow. At some point, the filter is plugged and must either be cleaned (if possible) or replaced. 

     Sediment Filters: Every RV Should Have One    If water quality is ever a problem for you, then you should always include a sediment filter as your first step in overcoming your problem. Even if murkiness is not your complaint, the sediment filter will protect your other downstream equipment from premature failure by removing the gunk that could otherwise cause a problem.

     How About My Taste and Odor Problems?
The contaminants that affect the taste and odor of water will go right through a sediment filter, so you'll need to add something else to remove them. The most commonly used method of cleaning up the taste and odor of water is passing it through a bed of activated carbon. The carbon has an uncanny ability to grab onto the bad stuff in water, leaving the water very clean-tasting and odor-free. Like a sediment filter, though, a carbon filter can only pull out a finite amount of contaminants, so it has a certain life expectancy. However, it is not possible to clean a carbon filter, so they must be replaced. Generally speaking, carbon filters will last twice as long as sediment filters, but they're also more expensive.

     What are NSF Ratings Used For?
The National Sanitation Foundation (NSF) is an organization that tests filters and rates them on their ability to remove chlorine from water. A filter must remove 75% to 100% of the chlorine to receive a Class I rating, 50% to 75% for a Class II rating and 0% to 50% of the chlorine to obtain a Class III rating. These ratings apply only to carbon filters.

     Granular Carbon Vs. Carbon Block Vs. Modified Carbon Block   Activated carbon, in the form of small granules, has been used for centuries to purify water. It works well and is still available in that form, but there is now another choice in carbon filtration. New technology enables manufacturers to produce filters in the form of  porous solid blocks, which are superior in every way to filters made of granular carbon. The latest technology in carbon filters is the so-called modified carbon block (MCB), in which filter blocks are built from fibers in a slurry of carbon particles. In order for any carbon filter to remove contaminants from  the water, the water must come into contact with the carbon. In granular activated carbon (GAC) filters, the water can create channels that enable some of it to pass through without being affected. In  solid block carbon (SBC)  filters, channels cannot form, so it forces the water to come into contact with the carbon. One result of this is that SBC  filters have a higher NSF rating than a GAC unit. Also, due to the way the carbon blocks are formed, the pathways through the block are very small, and SBC filters often have a small micron rating, which enables them to remove cysts and some other microbial pathogens.  All of this comes at higher price, of course, but many people find this product to be worth it. MCB filters are very similar in ratings to an equivalent micron model SBC filter.  They offer a better flow rate, longer life through increased depth capacity, and a variety of micron sizes, all at a price that is equivalent to the SBC units.  These carbon filters are very successful with RV use and for many RV customers, have proven to be the most effective and popular choice they can make.  They are naturally resistant to stagnation because of the fiber material they are made of.  The F5 and F1 models have become our best selling carbon cartridges by far.

      What is KDF and Why Would I Want It?   KDF is an alloy containing zinc and copper that can be incorporated into carbon filters to make them bacteriostatic. That means that bacteria cannot grow inside the filter. This is particularly good for people who use their RV intermittently, and do not want to empty their canisters of water as KDF will protect the filter while the RV is not being used. A word of warning, Solid Carbon block filters with KDF should be kept submerged in water for their life after installing into the canister. If they are removed and dried, they may seize up and not pass water on the next use. There are several other chemicals that manufacturers use to make their filters bacteriostatic, but many of them affect you as well as the bacteria!  KDF has a very good record as being the safest agent yet found for keeping bacteria from growing in filters, although silver nitrate is common, also.

Can I Get Sediment Removal and Carbon Filtration in the Same Unit?
Yes, you can. Many filters installed as original equipment on RVs and many replacements are so-called combination units, like our RV-C1 and RV-C2 cartridges. They are compact and relatively inexpensive, and they're made of carbon-powder-impregnated paper. The downside of these units is that they have a limited carbon component, so the taste-and-odor improvement is much less than you would get from a dedicated carbon filter. For better performance from a combination unit, we offer the F5 , F1 , and F1pb cartridges, which are modified-carbon-block units. All-in-all, the Sediment/Carbon Combination Filter is a reasonable solution for water quality problems, particularly if you only use your RV occasionally and wish to use a single external canister only.

What About Those Health-Threatening Contaminants?
This group has the potential for causing far worse problems than those discussed so far. They include biological  and chemical  contaminants, and they are more expensive to remove than the aesthetic contaminants. Even public water-treatment systems have trouble absolutely removing all of thesecontaminants. You can, fortunately, obtain protection from them by installing suitable equipment and processing your own water, even at home.


     Giardia, Cryptosporidium, E. coli - Yuck!
Biological agents include protozoa, bacteria, viruses, and cysts and spores. The most prevalent types of biological contaminants in water are very small particles with a diameter of 2 to 4 microns. One defense against these "bio-terrorists" is to remove them from the water. This is can be done with a very fine filter, and some of our solid-block carbon cartridges are capable of removing many biological agents. The best filter for this purpose, though, is a Doulton D-UC ceramic unit, with a rating of 0.9 microns absolute. This cartridge will filter out any particle that is  0.9 microns in diameter or larger, and will remove virtually all pathogenic microbes. Unfortunately, viruses are extremely small and difficult to remove. Many viruses will attach themselves to bacteria for a free ride, and these viruses can be removed by removing the "host". Some viruses, however, are "free-swimming" and are not attached to anything. Ultra Violet Systems are a good option if viruses are a big concern.

Total Purification - Is It Practical?
Total and complete purification of water is difficult and expensive. From a practical standpoint, it is not feasible for RV owners to achieve total purification. There are, however, two methodologies that can produce virtually pure water and are suitable for use in RVs.  The first one is distillation, but it is increasingly expensive to operate and produces a low volume of clean water. It also requires a lot of cleaning and maintenance. The second one is reverse osmosis, and we find this to be a very cost-effective solution that is more user-friendly than distillation.


     Reverse Osmosis - High-Tech Purification
Whole RV or Drinking Water Reverse Osmosis (RO) is a product of space-age technological innovation. It employs a semi-permeable plastic membrane to filter out most of the contaminants in water, including virtually all biopathogens, minerals and salts, and some other chemical contaminants. The membrane produces pure water and flushes itself with waste dissolved solids and contaminants.  The brine can be recycled, used to water plants, or dumped down a drain. The costs for this system are higher than regular filtration, but much less than buying bottled water (which may not be as pure as RO water anyway).