We have been using those screw-on tap filters for couple of years, and are considering moving to an under-the-counter water filtration system, so before putting out the big bucks, I figured some research was in order.
Before purchasing anything, it is fundamentally important to know what the local water contaminants are that the system must filter out, so that one does not overspend to remove something that is not in the water supply, and miss filtering out something important that is there.
In my Vancouver water supply, ozone is the primary method of water treatment, destroying the water-born micro-organisms. Chlorine is the secondary method of disinfection used in the distribution system, which means also Trihalomethanes (THMs) and Haloacetic Acids (HAAs), two carcogenic biproducts of water chlorination are in the water supply. Thankfully our water is not fluoridated. Lead from pipes in homes that were built prior to 1989 would need to be filtered out also. Well water out in the Vancouver Lower Mainland valley is frequently contaminated with arsenic, so get your water tested and choose your filter appropriately.
My primary concern will be to filter out the chlorine and its biproducts, the THMs and HAAs, which are poisons that not only kill our vital gut bacteria impairing our digestion and immune system, but are also linked to cancer (particularly bladder cancer) when consumed, inhaled, or absorbed through the skin. For this reason, whole-house filtration systems are best, as then bath water and shower water will be chlorine-free too. As they say, if it is on your skin, you are drinking it! The cheapest way to eliminate chlorine from water is to let it sit, but possibly you may be inhaling the chlorine instead.
There are many kinds of filters out there, so what to choose? Make sure any filter you select is certified by either NSF International, CSA International or Underwriter's Laboratories. Here are the advantages and disadvantages of various systems:
- Activated Charcoal (Carbon) Filters
- organic compounds like benzene
- trihalomethanes (THMs)
- Soluable Organic Compounds (SOCs) like pesticides and dioxins
- industrial solvents (halogenated hydrocarbons)
- polychlorinated biphenyls (PCBs)
- polycyclic aromatic hydrocarbons (PAHs)
- Volatile Organic Compounds (VOCs) like chloroform and petrochemicals
- Filter needs to be changed regularly
- Water flow reduces over time until filter is changed.
- Filters less well if water is hot
- Pour-through (water jugs) or faucet mounts work less well as water does not sit in filter long enough
- Can breed bacteria, so only appropriate for water bacteria-free water supplies
- Does not remove
- heavy metals unless specifically designed to do so, so read labels
- Reverse Osmosis
- total dissolved solids (TDS) and suspended matter
- nitrates – If sulfates and/or TDS levels are high, nitrate levels are not reduced
- inorganic compounds
- metals like arsenic, lead, copper, cadmium
- Usually comes with a carbon pre-filter, which filters chlorine etc. (see above)
- Use a lot of water – wastes 3 to 20 times the water being treated
- requires a storage tank to ensure adequate filtered water when needed
- Waste water adds more load to household septic systems
- more expensive
- Difficult to install – call a plumber
- May filter out too many total dissolved solids making the water too soft, causing body mineral loss
- Needs a pre-filter (often a carbon one) to filter out chlorine
- Needs regular maintenance and monitoring of membrane for leaks
- heavy like lead, mercury, chromium, arsenic, lead, cadmium, copper, selenium
- can be combined with a carbon system
- Removes all dissolved mineral solids making water too soft, causing a mineral loss in the body
- Water becomes too acidic, also damaging to the body
- Uses a lot of electricity, so expensive
- Ultraviolet Light
- bacteria and other micro-organisms
- Does not remove
- sediment and suspended matter
- Does not remove
- Removes bacteria and other micro-organisms effectively
- Concentrates metals
- does not remove
Villanueva CM et al. Meta-analysis of studies on individual consumption of chlorinated drinking water and bladder cancer. J Epidemiol Community Health. 2003 Mar;57(3):166-73.
Villanueva CM et al. Bladder cancer and exposure to water disinfection by-products through ingestion, bathing, showering, and swimming in pools.
Am J Epidemiol. 2007 Jan 15;165(2):148-56. Epub 2006 Nov 1.
Zwiener C et al. Drowning in disinfection byproducts? Assessing swimming pool water. Environ Sci Technol. 2007 Jan 15;41(2):363-72.
Chevrier C et al. Does ozonation of drinking water reduce the risk of bladder cancer? Epidemiology. 2004 Sep;15(5):605-14.
Online at CBC Marketplace Shopping for home water filter systems
Online at Metro Vancouver Water treatment process
Online at Water treatment guide
Online at NSF
Online at Reverse Osmosis
Online a Natural Resources Defense Council
Online at Fine Waters
Copyright 2007 Vreni Gurd