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Drinking Water Contaminant Removal Table

The Contaminant Removal Table itself begins just below the Key: The contaminants are listed in columns across the top of the chart.  Also indicated are      the type of contaminant; biological, inorganic, or organic. The treatment methods are listed in rows down the left side. At the intersection of a contaminant column and a treatment method row will be a     notation about the removal effectiveness of the treatment method on the contaminant. Important information about some topics are indicated by numbers throughout the table     linked to notes following the chart. Some of the contaminants or treatment methods have links to outside sources for     additional information. Other contaminants that would not fit across the table (turbidity, hydrogen sulfide, odor &      taste, acidity & alkalinity, and radon & radium) are discussed after the main table. This is by no means a complete list of all possible contaminants - there would be many      thousands.  I have included the more important and/or common contaminants in this list. It is important to actually know what contaminants are present in your water (or might be     introduced accidentally) before investing in a treatment method.  If you are on municipal     water, obtain and read your annual water quality report.  If you have a well or use surface     water, try to determine which contaminants are most liable to be present (try the local     EPA office, local health department, neighbors, local water companies, etc.) and have it      tested periodically. If this table is too large for your screen, I have broken it into two separate tables, one     covering the biological and organic contaminants, and the other covering the inorganic     contaminants.  They should be easier to read on monitors set at 800 X 600.

	Notes: 1  - Iron is a common nuisance contaminant mostly for people with their own wells, water treatment companies tend to remove it fairly effectively.  It can be found in a number of forms in drinking water, soluble, insoluble, organic, and as a contributor to an iron bacteria problem.  Go to the Iron in Drinking Water fact sheet from the Illinois Department of Public Health, Division of Environmental Health for more information.   Treatment methods for iron include:
	Iron filters - Iron filters are only useful for removing soluble iron and manganese; precipitated iron particles will quickly plug them. They appear similar to water softeners but contain a bed of natural or synthetic manganese green sand. Manganese dioxide oxidizes iron and manganese and the oxidized particles are then filtered out in the lower part of the bed.  The filter bed must be backwashed frequently to remove the accumulation of iron particles. For backwashing, a flow rate more than double the normal service flow rate is usually required. The exhausted manganese must be recharged by adding potassium permanganate.  Since the slime produced by iron bacteria will clog the filter, the iron bacteria must be controlled before using an iron filter.  Back to chart.
	Standard water softeners can remove small amounts of dissolved iron (5 to 10 ppm). With special resins and regeneration processes, up to 5 mg/l of soluble iron can be removed. Iron bacteria must be controlled before passing through the resins, since the slime produced by iron bacteria will clog the resin and reduce its effectiveness.  Oxidized iron (precipitated rusty sediment) must also be removed before treating with an ion exchange resin to prevent the resin from becoming clogged.
	Polyphosphate feeders - These units can handle up to 3 mg/l of iron in solution. They contain a phosphate compound which coats the soluble iron and prevents its oxidation when the water is exposed to air. The compound is not effective against iron that has already oxidized.  When some waters are heated, the raised temperature will reduce the effectiveness of the polyphosphate so that oxidized iron will accumulate in the water heater. The heated water will be rusty and unsatisfactory for many home uses. Polyphosphate is most effective in cold water.
	Chlorination and filter. Chlorination followed by filtration through a sand filter can remove any quantity of iron in any form. The chlorine oxidizes and precipitates the iron and the filter removes the particles. Carbon filtration may be required to remove excess chlorine.     Ozone will also oxidize the iron and manganese causing them to precipitate so they can be filtered.  Back to chart. 2 - The costs are very approximate because of a wide variety of factors.  Listed costs also do not include the initial expense of the treatment equipment. The ongoing costs listed are mostly useful for POU and bottled water users and are meant to give you a feel for the relative expenses you would incur over a period of time.  For example, bottled water at about $0.25 to more than $1.00 per gallon (much more if you purchase "designer" water) would cost at least 3 to more than 10 times as much as an equivalent amount of purified water filtered through a carbon block filter at about $0.05 to $0.10 per gallon.  If economics are important to you and you are using more than a couple of gallons of treated water a week, this information might be useful.    Back to chart. 3 - I am afraid I do not know anything about magnetic or electromagnetic conditioning of water.  I do not have a hard water problem and thus have not had a motivation to try the technique.  I have also not been able to get any unbiased information on the effectiveness of this treatment.  I listed it here because it is a widely advertised alternative to traditional water softening which is not particularly environmental (or health) friendly, and, if it actually works, would be a valuable addition to hard water treatment methods.  If anyone has first hand experience with these devices or knows of a link to an independent review article, please let me know, and I will report anything I discover.  Back to chart. 4 - Reverse Osmosis, Ceramic Filters, and Carbon Block Filters can have pore sizes of 0.5 micron or less (RO membranes are far smaller) which can remove many harmful bacteria very effectively.  It is best, however, not to depend on these treatments for your primary, ongoing disinfection method for water that is known (or suspected) to have harmful bacterial contamination.  A damaged filter element could allow enough bacteria into the "filtered water" stream to cause illness - and there would be no way to detect the problem without constant testing.  They are definitely reliable enough, however, to be used as a backup system with normally safe domestic water (in case of accidental contamination) or for water treatment in case of an emergency where normal water distribution is disrupted and the available water may be contaminated..   (Granular Activated Carbon) filters (because of the inconsistent pore size discussed below)  will NOT safely remove bacteria from drinking water.  You will see some of these systems marketed with embedded silver - this is to help prevent trapped bacteria from growing within the filter media.   I have not seen any independent tests on the ability of KDF filters to reduce bacterial contamination in running water.  From my reading, it appears that the KDF media prevents trapped bacteria from growing or multiplying.  Back to chart. 5 - Activated carbon, whether as fairly large granules, in granulated activated carbon (GAC) filters, or compressed into solid carbon blocks filters, is very effective at removing a wide variety of organic compounds.  I placed a S 5 for whole house and point of use GAC filters because 1) water moves through a whole house filter (unless it is enormous) too fast for complete removal of anything except particles smaller than the largest pore size (usually 10-20 microns), and 2) GAC filters, because they contain loose carbon particles and are prone to channeling, where the flowing water creates relatively large channels through the filter medium.  Water moving through these channels does not have much contact with the activated carbon, and thus, filtration of the channeled water is minimal.   However, if organic chemicals are a significant contaminant in the water entering your home, a whole house, GAC filter will help  reduce the level of these contaminants.  This is important, because many organics can vaporize in a shower, for instance, and be inhaled.  If you choose a whole house carbon filter, be aware of their limitations though, and seriously consider a Point of Use SBAC filtration system to treat your drinking and cooking water.  Also, if you have a yard or garden that is watered by your household water, and if it is at all possible, consider splitting your water line so unfiltered water is sent to your outside taps - otherwise you must change the filter much more often.  Back to chart. 6 - Iron bacteria are mostly a problem for people using wells water with high iron or manganese concentrations.  The bacteria themselves do not necessarily clog filters, but the brown slime they produce may.   None of the POU treatment devices would be effective for the treatment of iron bacteria.  If this is a problem, one of the methods described below should be used to remove the bacteria and "slime" before the water reaches a POU device. The Wisconsin Department of Natural Resources Bureau of Water Supply has a site, Iron Bacteria Problems in Wells, that provides additional information about preventing and treating the problem.  7 - All ion exchange resins work by exchanging the contaminant you wish to remove with one that is less harmful or annoying.  Water softeners usually exchange salt for the calcium and magnesium in the water.  Salt concentrations are usually low and not a health concern, unless you are on a restricted sodium diet.  The residual salt or other exchange chemicals eventually get dumped into the septic system or sewer, however.   There are several types of ion exchange resins available to treat different water contaminants, cation (water softeners - removes positively charged ions), anion (removes negatively charged ions like nitrates and sulfates), and mixed bed resins containing both cation and anion resins.  Back to chart. 8 - A RO systems should come with a pre-filter (a sediment filter and perhaps a chlorine filter) to remove contaminants that would damage the RO membranes.  A Reverse Osmosis filtration system should also come with a high quality Activated Carbon filter to remove organic and some inorganic compounds that are not removed by the RO membranes.   Read note 4 for information about microbial filtration.  Back to chart. 9 - Water usually contains dissolved gases and may contain other substances, like some of the organic chemicals, that can be volatilized at temperatures below the boiling point. When the boiling point of volatile chemicals is near water, it is difficult to separate these materials from water using distillation. In addition, the separation of steam from the liquid that contains dissolved solids is not absolute. Minute amounts of the dissolved materials will be carried along with the steam. Distillation normally removes over 99.9 percent of many dissolved materials.  A gas vent, fractional column, or carbon filter should be included with any distillation system you purchase to remove the volatile contaminants.  Back to chart. 10 - Ultraviolet (UV) light is capable only of disinfecting water, no other contaminants are removed.  Different pathogens require different doses for treatment (cysts require a higher dose than most bacteria, for example), so make certain any UV system you consider is capable of killing the specific microbe(s) you are concerned about. In order for UV disinfection to be completely effective, the water coming into the UV chamber must be extremely clean.  Any particulate material may "shadow" the pathogens and allow live microbes to exit the UV system.  Back to chart. 11 - The list of water contaminants and available treatment technologies can be rather overwhelming.  After all is said and done, though, a high quality, Solid Block Activated Carbon filter (SBAC) (designed to remove the most common drinking water contaminants) would be my recommendation for probably 80%+ of people concerned about their drinking water quality - the other 20%,or so may have more serious contaminant problems, and will need to explore more complex (and expensive) treatment solutions specific to their situation.  After considerable research, a Solid Block Activated Carbon filter was the solution I selected for my home. My strategy was to figure out what contaminants were actually in my water (or might be released into my water due to an accident) and then choose the treatment method: 1) that would reliably remove those contaminants, 2) had the lowest operating and maintenance costs over the 30 - 40 years I planned to use it, and 3) be the easiest to use and required the least maintenance. Denver municipal water, like water from most medium to large public water sources is very good quality overall, but it contains chlorine and disinfection byproducts (DBPs).  Even though the DBPs were present at levels below the EPA maximum contaminant levels, they were still of concern because of the health risks of long term exposure (discussed elsewhere on my site).  Although I did not test for lead, I strongly suspected it was present in our 55 year old home, because (as discussed elsewhere), lead is quite prevalent in both new and older homes.  Contaminants I was concerned might be released into the water because of an accident included E. coli, giardia or cryptosporidia cysts, and possibly some organic contaminants like MTBE.  Arsenic, and other harmful inorganics, like nitrates, cadmium, etc. were very unlikely to ever be our municipal water in significant or harmful quantities.  Other Organic contaminants like pesticides and solvents were also unlikely to ever be present, although a SBAC filter will remove wide variety of organic compounds. There were four available technologies that would fairly simply remove all the contaminants that I wanted to protect my family and me against; Bottled Water from a certified company, Distillation, Reverse Osmosis, and Solid Block Activated Carbon filters.  Of these four treatment methods, SBAC filtration systems were easily the simplest to use and maintain (normally one filter change every year or so).  SBAC filtration also had the lowest ongoing costs at about $1.00 per week for up to about 14 gallons of purified water per week ($2.00 a week if you filter 14-28 gallons/week, and so on). Most people using regulated municipal water will have home water characteristics similar to mine - fairly clean, biologically safe water with known contaminant levels, and a low risk of accidental contamination.  A SBAC filtration system would be an ideal choice if this describes your water.  Even if you soften your water, a SBAC filtration system would be a good addition to your treatment plan, because softening, by itself, does not remove any contaminants harmful to health that might be present.  People using well water with the same characteristics as described above would also benefit from the protection of a SBAC filtration system.  Back to chart.

Final thoughts and disclaimer:
In the table and notes above I have attempted to summarize the most common treatments for the most prevalent and important drinking water contaminants you are liable to encounter.  The notations indicating which treatment method removes which contaminant are as accurate as I could make them after reviewing many sources, but you will need to carefully double-check any decision you make regarding a treatment method with the manufacturer from which you plan to purchase the treatment unit to make certain that it is certified do what you expect it to do.  Three reasons for double checking: 1) an error may have been made by me or by one of my sources.  2) Technology changes rapidly, so there may be newer methods on the market than I am aware of, and 3) all treatment "units" are not created equal - for example, there are several thousand filtration systems on the market.  Some reliably remove a wide range of inorganic and inorganic contaminants while others remove only a couple.  Also, filters from some uncertified companies may have chronic manufacturing defects that render them useless.  
The best protection for purchasing a filtration system or bottled water is to make certain it is certified by a third party to perform as advertised.  NSF International is a group that certifies water treatment systems, distillation units, bottled water, water softeners, and a number of other food preparation systems.  NSF certification means that not only do the products perform as tested, the product advertisements are also evaluated for accuracy and truthfulness.  Products are tested on an ongoing basis to make certain that companies continue to produce products that perform as advertised.  The bottled water industry regulates itself through the International Bottled Water Association (IBWA). Bottled water FAQs. The IBWA sets manufacturing requirements, which help to ensure that bottlers meet FDA health standards.

Any person who requires water of a specific microbiological purity should follow the advice of their doctor or local health officials regarding the use and consumption of tap water treated by ANY purification system.

Other considerations for purchasing a water treatment system (or bottled water)
-Is the treatment appropriate for the problem? For example, with hard water the equipment must remove calcium.
-Is the treatment cost effective?  If you plan on using it more than a couple of years, the ongoing and maintenance costs can far outweigh the initial cost of the filtration system.  Bottled water, for instance, has continuing ongoing costs while a filter might have a high initial cost but cost very little to maintain over the next 40 years or so.
-Is the equipment guaranteed?
-How long has the vendor been in business? Do they have a good reputation?

Copyright © 2001 Randy Johnson. All rights reserved.
Revised: May 04, 2006