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Filtration / Purification Technologies Available to Homeowners

 Mechanical / Sediment Filtration:

This is the typical household “Water Filter”. Removes sediment only UNLESS; the pore size is less than 0.4 microns (1/25,000”; Human hair ~100 microns). IF the pore size is less than 0.4 microns it also removes sediment, cysts and bacteria. Typically installed are 5 to 50 microns.

Granular Activated Carbon

One pound of carbon contains a surface area of 125 acres and can absorb thousands of different chemicals. Disadvantage: does not remove many inorganic toxic chemicals, or bacteria, viruses, parasite cysts, and if not properly maintained can become a growth medium for microorganisms.

Solid Carbon Block Filters

This technology has combined the adsorption capability of carbon discussed previously with the ability of a solid brick of material to selectively strain out particles from water forced through it. Disadvantage: does not remove many inorganic toxic chemicals, or bacteria, viruses, parasite cysts, and if not properly maintained can become a growth medium for microorganisms.


Distillation is a process that heats water to the vapor point then condenses it, leaving behind mineral and many metal and organic contaminants. Disadvantage: does not remove all organic compounds and especially VOC’s (volatile organic compounds), requires electrical power to work, and water must be stored.

Reverse Osmosis

Reverse osmosis, or RO, is another separation process that makes use of a semi- permeable membrane. This membrane lets particles of a certain size or smaller (water) through and keeps back larger particles (most contaminants). Disadvantages: Requires good pressure, wastes some water, must be carefully monitored for integrity, and is fairly expensive. If a pump is used, it requires electrical power to operate.

Ultraviolet Light

Ultraviolet light systems make use of the ability of ultraviolet light to kill bacteria. Such systems are effective on bacteria, viruses and some algae. Disadvantages: water must be very low in turbidity for light to be effective, proper wavelength filter must be used and requires continuous source of electrical power to function.


Ozone units super-oxygenate water which kills bacteria with adequate contact time. Disadvantage: more expensive than chemical disinfection and requires continuous source of electrical power.

Chlorination and other Chemical Treatments

Effective for reaching internal components of water distribution and purification systems. Damages some water purification devices. Over chlorination can produce toxic chemical byproducts especially in the presence of organic matter.


Table A. Typical Water Quality Problems and Recommended Treatment Systems


Recommended Treatment Systems

Bacteria and other microorganisms


Taste and odor

Activated Carbon (charcoal) filter

Hydrogen sulfide gas (rotten egg odor)

Oxidizing filter followed by carbon filter; chlorination followed by sediment filter

Sediment (suspended particles)

Spun Fiber filter (Mechanical Filter)

Hardness (calcium and magnesium)


Dissolved iron

Softener for up to 5 milligrams per liter); Iron filter; chlorination followed by sand filter and carbon filter

pH (acid or alkaline conditions)

Neutralizing filter or chemical-feed pump

Organic chemicals (pesticides, fuel products)

Activated Carbon (charcoal) filter

Metals (lead, mercury, arsenic, cadmium), and other minerals (nitrate, sulfate, sodium)

Reverse osmosis unit; distillation

Water Treatment Steps: The Recommended Order

(if this order is not followed, the treatments themselves will likely be ineffective)

1. Have water tested

2. Remove sediment

3. Disinfect

4. Remove H2S and odor-causing substances

5. Remove Iron and Manganese

6. Treat for hardness

7. Neutralize acidity

8. Remove VOC's and SOC's - organic compounds

9. Remove heavy metals, lead, mercury, arsenic, cadmium, etc

10. Kill any bacteria, parasites, viruses etc using UV or Ozonation

Click here to see a consumer report research article comparing various filter systems they tested.


If you have an existing filtration system please consider the following:

Many people have had various filtration systems installed in their homes. They often believe that because these systems "filter" their water that they also "purify" their water. They believe that "crystal clear" means pure. This is often completely untrue. Many filters are designed for removing sediment, but do nothing to make the water safer to drink, and this is precisely the kind of filter that is installed in most homes by building and well drilling contractors. Find out exactly what your system does, and if you can't, we can help you find out so you'll know for certain.

Filtration systems become less effective with age. You may want to test the effectiveness of a system you have had installed to determine if it is still working properly. A single heavy rain event can produce enough turbidity in the water to inactivate certain types of filters. Channeling can make other filters ineffective.

Some of the more common Factors Affecting Filter Performance are:


The filter media loses its ability to remove contaminants and allows contaminants to move through without being adsorbed. When this happens there may be no detectable difference in the output water (the water you consume) but testing will almost always allow us to detect filter exhaustion.



Certain types of filters, those that are filled with particles (ex. sand, activated carbon etc.) can develop channels as water moves through the filter along the paths of least resistance. These channels then allow water to move through the filter without coming in contact with the purifying medium. Water is essentially untreated. Again, there is often no obvious warning or sign that this process has occurred but testing will reveal this deficiency.



If sufficient sediment is brought in through the water coming into the filtration system it can block all the channels and cover the purifying medium in the filter. This is often detected by slowing or reduction of flow through the filter system, but can escape detection if flow rate is only slightly affected. Again, testing will reveal this deficiency if flow is not significantly slowed, because the filter no longer functions to purify the water properly.



Water conditions such as pressure, pH, temperature, or other factors can change suddenly. It can happen due to processing steps at the water treatment plant, or sudden changes in water pressure due to an inadequate water system, pump failures, or breaks or leaks in a water main, or sudden changes in temperature due to freezing etc. These sudden changes can cause carbon sludge which has collected on certain types of filters (during the process of removing contaminants) to be dumped back into the water passing through the system. That is, the contaminants captured on the filter are released into the water you will be drinking after it passes through the filter. This often produces a temporary discoloration (usually darkening -sometimes with granules visible) of the water coming from the filtration system. If this happens, the filter needs to be changed promptly. If the amount of contaminant released into the water is not very large, you may still be drinking unpurified or worse yet, contaminant-enriched water, without noticing. Guess how this can be detected? Yes, our tests can find this kind of problem.


We can recommend water treatment processes and regimens that can guarantee the water you consume to be completely safe to drink.


Work done by Kentucky Dept of Agricultural Engineering for the USEPA

Knowing which filter to purchase

We do the research and know which filters are the best based on available data ... so our recommendations are NOT driven by which brand we sell



  1. Some filters are much better than others at removing contaminants

  2. We DO NOT sell filters, so we can tell you which is the best

  3. If you don't need water purification, we will tell you

  4. We test to find out which, if any contaminants you may need to remove - you may not need any purification for Puritek brand devices and systems or for Everpure Systems  for Kinetico


online guide  Barnstead International Research Grade Water Purification  Health Store for selections of different brands for information about certification of purification devices


North Georgia's Only Independent Water Treatment Professionals


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Last modified by Dr. Eberhard Essich 03/22/17