Why is chlorine in my drinking water?
Chlorine has been used to disinfect water for consumption in the US since the early 1900's, leading to the virtual elimination of waterborne diseases and improved public health. It is extremely effective at killing pathogens and diseases, is inexpensive, easy to control and monitor, as well as it easily maintains a residual level in the water distribution that continues protecting drinking water supplies from pathogenic bacteria and organisms. This is why chlorine is considered one of the best disinfecting agents.
If you have a private well then this may or may not be what you are using to disinfect your water supply, and you do have some choice in the matter. Some methods are ultra-violet, distillation, reverse osmosis, and chemical feeds (bromine, chlorine, chloramines, iodine, ozone, and etc.), but cost, availability, and your local water quality will be driving factors in the selection process.
What are problems associated with having chlorine in my drinking water?
The most obvious problem with chlorine as a disinfectant is that it can leave an unpleasant taste or smell, it dries out your skin and hair, as well as it alters the taste of your drinks (tea and coffee!). Chlorine isn't a carcinogen and not considered hazardous or harmful in the amounts used in our water supply.
The potential issue with chlorine is that it will form disinfectant by-products (DBP). However, any type or form of chemical disinfectant used is going to have one form of DBP or another. This is all dependant on your specific water quality, methods of water treatment, and any number of other factors relevant to your area. Some of these DBPs are, or are thought to be, carcinogenic, while others will not be at all.
Water quality will also change based on the season and other variables and is rarely the same year-round (there are some few places that have wells that are both deep and old with little seasonal change throughout the year). If you are on a well, your water quality may not be being monitored at all and will probably change more frequently without being noticed. Whereas "city water" will be treated based upon the water quality at that particular time it is monitored and tested. There are water quality regulations that must be met to ensure the water is drinkable. This means that the use of chlorine may increase or decrease, based on the results of the water quality test at that time.
How can I remove or reduce chlorine from my water?
Great-tasting water, with no odor, can be achieved using granular activated carbon, carbon block filtration, and/or membrane filtration (reverse osmosis filtration). These filters control and remove chlorine and odors from your drinking water supply and are typically installed at your point-of-use (POU). Your POU would be your faucet, therefore the filter system would be installed either above or below the counter. There are also the larger point-of-entry (POE) filtrations systems, meaning the whole house is filtered.
How does carbon filtration work? Reverse osmosis filtration? Which is better?
Carbon filtration is a very simple principle; it adsorbs chlorine (as well as many other impurities and odors), leaving no negative effects on your water supply. Adsorption takes place when your water comes in contact with the carbon filter. The carbon attracts the chlorine molecule from the water and it adheres to the surface of the carbon. A few factors that will influence the adsorption of chlorine is the temperature, pH balance and contact time. Adsorption of chlorine works best in the ranges from 40-55 degrees Fahrenheit (this is pretty typical unless you have warm surface water as your supply water) and with pH levels below 7.0. The contact time is something that really makes a difference with filtration. Mainly, the longer your water has contact with the carbon, the more chlorine molecules that are removed. So if you have a lot of chlorine, you'll want more contact time (slower flow and higher micron rating), although this does effect how much adsorptive surface area that is available. Once a carbon filter is "full", then it will no longer be effective and will need to be replaced.
For filtration, carbon comes as granular activated carbon, carbon briquette (block), carbon-impregnated cellulose, and as a loose-type media. These are basically all cartridges with the exception of the loose carbon media* which comes in a large sack, not unlike rice or potassium. Each cartridge has slightly different variances in filtration size, how much they will be able to adsorb and how long they should be used (because they will eventually become "full" and not be effective any longer). Generally a lower micron rating (the lower the micron the more impurities that are filtered out) with lower flow rates (maximum contact time for greater filtration) will provide you with the best tasting water. You will find that the carbon block is the "best", followed by granular activated and finally carbon impregnated filters.
* - Loose carbon media is used in much larger whole house filtration systems (POE), which is more complex and typically a part of your private well water treatment system. Cartridge filters are not able to do this and so are used as a single-use filter, and are then quickly and easily replaced.
Reverse osmosis filtration is one of the highest levels of filtration that you can perform, and are also much more complicated than the carbon filters. Reverse osmosis systems operate much like our body's organs do (only in reverse), by forcing water through a thin membrane in the filter system removing nearly all particles leaving only pure water. There are grades of filters and each is rated by the amount of water desired on a gallons-per-day basis. Residential reverse osmosis filter systems come as 2, 3, 4, or 5 stage systems. This means that they have one membrane filter with other filter types added to help condition the water. They will always have a carbon pre-filter. You can then add a post filter and a sediment pre-filter followed by another carbon pre-filter to get to the 5 filtration stages. The reverse osmosis membrane by itself will not be able to remove chlorine. In fact, chlorine will actually destroy the membrane which is why the carbon filters come with the system. Add to this that you also need a bladder tank and a special water filter faucet with an air gap for it to all run properly. Not to mention that you should also have water that isn't harder than 3 grains per gallon, a water supply that is at least 35psi and pre-treated. A reverse osmosis filter system will also require annual maintenance and regular changing of filters and membranes (based on water usage) for it to function properly.
Deciding which is "better" is certainly a personal choice tied to how much (or little) you want to filter out, what your local water conditions are and how much time you want to invest to maintain the unit (or having it professionally maintained for you).
The carbon filters are great for removal of chlorine taste and odor and are a great value for the cartridge filters used for POU. They also come in larger sizes for whole house (POE) applications as well as the loose media filter systems. The loose media type is a little more complicated while the larger cartridges are less efficient than the smaller POU filter systems, but are great for removing bad taste and odor from your entire system (typically, they will have greater contact times and capacity).
The reverse osmosis filter system is much more than your typical water filter. It has a higher cost both initially and for ongoing maintenance. It also requires you to understand more about water quality and to test your own water (unless you're paying for this as a service). However, it will provide you with nearly pure water to drink and you will be certain to protect your family from any possible contaminants.