The Water Blog Drinking Water Issues #2
Water Disinfection vs Filtration - What is the Difference?
Posted on April 20, 2014
There are many technologies available to filter your drinking water at home.
Some of the more popular methods include cartridge filters both for whole-house and those that mount on-the-faucet, water softeners, reverse osmosis (RO) systems and ultraviolet (UV) systems. This article offers a brief discussion of the differences between the technologies with the intention of helping you select the appropriate equipment for your water purification at home.
Physical filtration of water is a relatively simple concept. Consider a coffee maker that uses a plastic basket and a paper filter. The paper filter simply physically prevents the coffee grounds from passing into the coffee pot - this is the principal behind all physical filtration methods.
A sediment filter is a good example of physical water filtration. These filters are available in different configurations such as cartridge style or auto-back-washing style, but they all work by physically removing or skimming contaminants in the water and holding these in the filter material (just like the coffee filter does). Rust, dirt and dust are some of the most common contaminants that sediment filters remove from water.
Carbon filters are a bit of a different story. Although they can and do remove particle contaminants (like a sediment filter) these filters are designed to help remove contaminants that are hard to remove just by skimming. The carbon material in these filters is capable of absorbing contaminants from the water itself rather than just skimming materials that happen to be floating in the water stream. Carbon media is available in various configurations for various specialty jobs but most commonly is used to remove foul taste and odour from the water along with some types of chemical contaminants such as chlorine and some heavy metals such as lead.
Both sediment and carbon filters are available in various styles. Physical filtration of drinking water including both sediment filters and carbon filters where appropriate, is the simplest method of increasing the quality of your water supply at home. However it must be noted that physical filtration does have it's limits and these filters typically cannot remove other contaminants and pathogens that may affect your water source.
A water softener is a specialty piece of equipment that will "soften" your water by removing the calcium which makes water "hard". Soft and hard water have both advantages and disadvantages. On the positive side "soft" water feels good on your skin while showering. It can make your skin feel silky and will allow detergents to do a better job of cleaning. On the other hand, many folks do not wish to drink "soft" water because in the process of softening, the water, calcium ions are replaced by sodium ions and many people do not wish to add to their sodium consumption for health reasons. A water softener can also perform some filtration functions such as removing small amounts of iron from the water.
A reverse osmosis water treatment system is a specialized piece of equipment that uses different technology and is not technically a filter. The RO process involves applying pressure to move water through a membrane to remove dissolved contaminants. The most common use of RO is for the desalination of sea water. Household RO systems usually combine physical filtration along with RO and other technologies in order to create a complete water treatment system. The RO process though highly optimized to create pure water, is also highly wasteful. Many household RO systems recover only a small fraction of the water entering the system and the rest goes down the drain.
The typical RO system used in the home will not only remove contaminants from the water, it can also strip many of the minerals in water that may be required for optimum health. Often the taste of RO water is termed "flat" as most of the mineral content that gives water it's "taste" have been removed. RO systems can efficiently trap pathogens such as E.coli and coliform, however trapped bacteria often tends to build up on the membrane and this may cause contamination problems should the RO system malfunction.
An ultraviolet (UV) light water treatment system is typically designed to accomplish two functions. First the UV system will usually be configured with a physical filtration system normally fitted with both a sediment filter and a carbon filter. The idea is to pretreat the water to clarify it for further treatment in the UV lamp chamber.
Once inside the UV chamber, water is subjected to intense UV light that is designed to kill any potential pathogens in the water including E.coli and dozens more. This pathogen kill is virtually instantaneous and does not require a holding tank or other methods to store the water for future use. In fact, UV systems are designed to work in "real time" meaning that the water is treated to kill pathogens as it flows through the UV chamber and to your faucet.
A UV sterilizer will not remove dissolved contaminants in water (such as salt) and it will not waste any water either (100% of the water going through the UV chamber is delivered to your faucets). The function of a well designed UV system is to physically filter the water to a degree that is aesthetically pleasing, and to a degree that will allow plenty of UV light to penetrate the water stream. The cleaner the water entering the UV light chamber, the better the disinfection process will be.
In summary, it's relatively easy to determine what type of water filtration system will best suit your needs. Physical filtration will improve the aesthetic appeal of the water including clarity and taste/odour issues. A water softener will remove calcium and the "hard water" scale that may be accumulating in your plumbing system. RO systems will remove dissolved contaminants such as salt from seawater but are highly wasteful of water and may not be the best choice for "typical" residential water treatment. A UV sterilizer will typically combine physical filtration with protection from pathogenic contaminants using natural UV light. This type of system (possibly combined with a softener) is generally seen as the most cost efficient for most households using surface water, municipal water or well water as the source of drinking water in the home.
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