SMI Analytical Laboratory Services | Types of Water Filters | How Water Filters and Water Purifiers Work


SMI Analytical Laboratory Services :: Water Testing :: Water Analysis

Types of Water Filters for Drinking Water
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Is the Water Filter You Own or are Buying The Right Water Solution For You

Many people own Water Filters and Water Purifiers that are not suitable or are often not required. It is important to understand what water filters do. More importantly it is for you to understand what water filter or water purifier you require, If Any!

The Most Common Types of Water Filters Include

  • Active Carbon or Charcoal Filters
  • Ultra-Violet Sterilization
  • Cartridge Filtration
  • Reverse Osmosis
  • Ion Exchange Resins
  • Ceramic Filters
  • Combination Units using one or more Water Filtration Technique

  • Active Carbon or Charcoal Filters

    Typical Contents Of Household Filter Cartridge............Electron Microscope View of Pores in Active Carbon
    Coconut Husk Active Carbon Magnified view of Active Charcoal Demonstrating Millions of available Pores

    If one looks at the photograph on the left one can see why the other term for Active Carbon is Active Charcoal. The term "Active" is used to describe carbon's absorbing ability. If the pores become blocked the carbon is no longer active.
    If one looks at the Scanning Electron Microscope picture on the right, the internal surface area of active carbon is generally greater than 400 square meters. It is on this large available surface area that pollutants like Chlorine, pesticides etc. adhere to the carbon. The longer the contact time between water and Carbon, the better the removal of water contaminants.
    One of the draw backs of Active Carbon is it often becomes a breeding colony for various bacteria over time. One should ensure that there is post-sterilization, of drinking water if bacteria is a problem in water supply. Some people claim that impregnating the Active Carbon with Silver prevents Bacteria from passing through the filter. This claim is based on Silver's anti-bacterial properties. There are both believers and people who have there doubts about Silver impregnation in the water analysis community.
    Did you know your body will absorb more chlorine, in a Ten minute shower through your skin, than it will absorb from drinking 8 glasses of typical muncipal water

  • UV Sterilization

    UV Sterilization works on the principle that DNA and Proteins absorb UV radiation ( typically around 254 nM ), this causes the bacterial DNA to denature and renders them inactive.
    A typical UV Sterilizer

    UV supplies a relatively cheap source of Microbial contamination in water, Care must be taken with water that fouls Quartz Sleeve, with deposits, this prevents UV radiation from reaching water. Regular checking of Quartz sleeve and UV lamp is recommended. Where high levels of Iron and Manganese are present in water, longer exposure to UV is suggested.
    UV filters/sterilizers for drinking water should have a minimum radiation dose of 30mJ/cm2 at the furthermost point from lamp to ensure bacterial Inactivation. Secondly ensure lamp has quartz sleeve, if UV lamp is in direct contact with water, and for some reason had to break, not only would you be exposed to broken glass, but also to Mercury which is typically present in UV discharge lamps.
    SMI is one of many Labs worldwide that are researching various Nano-Sized Catalytic Inner coatings to enhance the effect of UV filtration, by the creation of Hydroxyl Radicals, on the Housings inner-surface. Hydroxyl radicals are more re-active than chlorine, and there breakdown products are water and carbon dioxide, both of which are harmless. Pesticides and other organic hazardous chemicals are broken down by Hydroxyl radicals.

  • Reverse Osmosis Filtration

    Reverse Osmosis Process A typical Multi-Stage RO Unit
    Reverse Osmosis is typically the most effective of your household units if used as a multi-filtration system combining particle filtration and Active Carbon. If your problems are with dissolved elemental salts in water, RO is the preferred option.
    RO units are not normally required with muncipal water systems, as bacterial contamination is most often the problem worldwide, and although RO units will "reject" bacteria, because of small pore size of membranes, tears and faults as well as manufacturing defects can allow some contaminants to pass through. No RO unit will provide "pure" water on a typical muncipal water supply. This indicates that some "contamination" does indeed pass through membranes. And final water polishing stages would be required to ensure "pure" water. Points to consider are that costly membrane can get easily clogged, beneficial minerals as well as "possible" water contaminants are removed. RO units are normally only for one drinking tap and do not cover household water. RO units waste a lot of water, have a look at flow to drain from RO unit.

    Membrane blocking, causing diminished flow into storage tank.............Bacteria on membrane
    Membrane Blocking creating a impermeable layer. Bacteria are unlikely to pass through membrane
  • Ion Exchange Resins

    These are either mixed bed or consist of separate anion and cation columns. Usually after RO unit or other water filter to "polish" water to a fairly "pure" quality.
    Some separate column units can be re-generated hundreds of times with an acid and alkaline wash. They don't produce waste water, but will need regeneration regularly if water contains high total dissolved salts( TDS ).

  • Ceramic Filters

    Typical Urn-Style Cermic Filter

    Ceramic water filters if correctly manufactured, have a pore size 0.22 uM or smaller. This prevents bacteria from passing through filter. Some can be cleaned and might provide the cheapest answer for bacterial free water. However if feed water has suspended particles present they tend to clog up leading to a diminished water flow. The typical gravity fed system supplies only a few litres per day. They are often combined with Active Carbon in Filter to provide a improved water filtration system.

    Water Information Pages from SMI:

    Questions to ask and points to consider before buying a water filter or water purifier.
    This page contains useful information on Devious Water Filter Salesmen, and how to handle them.


    Water is the major constituent of our bodies. Therefore the quality of the water we drink is very important for our health and well being.
    Feel free to Contact us with your water testing requirements and a quotation will be forwarded to you.

    Disclaimer: The liability of SMI ANALYTICAL is limited to the cost of analysis. SMI ANALYTICAL indemnifies itself from any legal action which may be instituted against it due to supplied data. SMI ANALYTICAL accepts no responsibility whatsoever for any results released, however used. No part of this document may reproduced in part or in full unless permission from SMI ANALYTICAL is granted in writing. This document may not be altered in any way whatsoever and is printed without correction.

    Water Chemistry Links

    Water Chemical Properties
    The mystery, art and science of water
    Why is water blue?
    Water Institute Southern Africa
    All About Water Purification
    Water analysis link
    Information on Water at TheWaterPage

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    SMI Analytical Laboratory Services / Chemical Laboratory Services specializes in quantitative X-Ray diffraction water analysis, water quality, drinking water, potable water, water tests, borehole water, water testing lab, water checking laboratory, water filters, water purifiers, laboratory, South Africa, in, near, site:, =, '', SA, za, 'loc:za
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    SMI Analytical Laboratory Services | Types of Water Filters | How Water Filters and Water Purifiers Work