There are several ways to remove chlorine from water for drinking, aquariums, brewing, or plants. Boiling removes chlorine from water. So do evaporation, water filtration with activated carbon, chemical treatments, distillation, and reverse osmosis. Here is a look at the pros and cons of dechlorination methods and whether they also remove chloramine.
| Dechlorination Method | Pros | Cons | Removes Chloramine? |
| Evaporation | Easy Inexpensive | Slow (overnight) Not suitable for large water volumes | No |
| Boiling | Easy Fairly quick | May require cooling before use Not suitable for large water volumes | No |
| Activated carbon filtration | Easy Fairly quick | Filter media requires replacement More expensive than evaporation or boiling | Maybe |
| Chemical treatments | Easy Quick | Moderately expensive May release undesirable chemicals | Maybe |
| Distillation | Highly effective Removes most impurities | High initial cost Slow | Yes |
| Reverse osmosis | Highly effective Removes nearly all impurities | High initial cost Slow | Yes |
About Chlorine
Before getting into ways to remove chlorine, it’s helpful to understand what chlorine is and the forms it takes. Chlorine is a nonmetallic element. In its pure form, it’s a greenish-yellow gas. In water, it’s a dissolved gas. This form of chlorine is toxic to aquarium denizens and plants (and humans, at higher levels).
Chlorine also occurs as its ion, Cl–. This is the form of chlorine you get when salt dissolves in water. It’s essential for life and isn’t typically a problem in water.
Chlorine also occurs in chemical compounds. Chloramine is an example of a chlorine compound. It forms when chlorine reacts with ammonia. Chloramine is toxic to fish, invertebrates, and plants, but it’s usually at a low enough concentration that it isn’t a serious threat to most people. Chloramine is a respiratory irritant and carcinogen. But, chlorine is also a respiratory irritant and reacts with some water impurities, forming toxic compounds.
Most cities treat water supplies with either chlorine or chloramine as a disinfectant. While chlorine is more common, the U.S. EPA says over 20% of Americans use chloramine-treated water.
Remove Chlorine by Boiling Water
Boiling water drives dissolved gases, including chlorine, into the air. Boiling water for hot drinks removes chlorine. But, boiling effectiveness depends on water surface area. So, boiling a large pot of water removes chlorine more quickly than boiling a narrow column of water. Boiling isn’t a practical dechlorination option for large volumes of water. Boiling does not remove an appreciable amount of chloramine, unless you boil the water a long time (~20 minutes).
Dechlorination by Evaporation
Like boiling, evaporation removes chlorine from water. The process is slower and depends on surface area and water temperature. Warmer water releases dissolved gases more quickly than cold water. To dechlorinate water, leave a bucket of water exposed to air overnight. Aerating the water with a bubbler speeds the process. Evaporation works great for dechlorinating water for drinking, brewing, and aquariums. But, it’s not a practical option for quick dechlorination or for large water volumes. Evaporation does not significantly remove chloramine.
Remove Chlorine With Activated Carbon or Charcoal
Filter cartridges for water pitchers, under-sink filters, and aquarium filters include activated carbon or charcoal. These filters remove chlorine. Certain activated carbon filters remove chloramine, but many do not. It’s important to read the product label.
Carbon particle size matters, so the most effective filters are typically the slowest filters. Dechlorination also depends on temperature. Activated carbon filters lose about half their dechlorination effectiveness as water becomes very cold. Alkaline water requires more activated carbon than acidic or neutral water.
Probably the biggest disadvantage of activated carbon filters is the need to replace filter media. Filter cartridges aren’t necessarily expensive, but they also aren’t interchangeable.
Remove Chlorine With Distillation
Distillation effectively removes chlorine and chloramine. It does not remove all other contaminants. The advantages of distillation are its effectiveness and relatively low cost. But, it requires an initial equipment purchase and is relatively slow. Freshly distilled water often requires chilling before use.
Remove Chlorine With Reverse Osmosis
Reverse osmosis is the gold standard, as far as water purification goes. It removes chlorine, chlorine, ammonia, and pretty much any other chemical contaminant. The process also filters out pathogens and particulates. The downside is that its expensive, slow, and releases a lot of waste water.
Chemical Treatments
Commercially-available chemical treatments remove chlorine and sometimes chloramine and ammonia. These products offer quick, easy dechlorination for aquariums and sometimes for brewing. Typically, they contain sodium thiosulfate, sodium hydroxymethane sulfinic acid, or sodium hydroxymethanesulfonate. Some of these products lower dissolved oxygen in water and harm biological filters.
Vitamin C (ascorbic acid) and sodium ascorbate also neutralize chlorine and chloramine. Vitamin C slightly lowers water pH, but isn’t toxic and doesn’t lower dissolved oxygen as much as sulfur compounds. One disadvantage of vitamin C is its relatively short shelf life.
How to Remove Chloramine
Chloramine does evaporate out of water, but its vapor pressure is much lower than that of chlorine, so the process is slower. Hot water releases chloramine more quickly into air than cold water, but boiling and evaporation are not very effective removal methods. Some activated carbon filters remove chloramine, but most do not. Some chemical treatments remove chloramine. Both distillation and reverse osmosis remove chloramine from water.
References
- Darnall, C.R. (November 1911). “The purification of water by anhydrous chlorine”. Am J Public Health. 1 (11): 783–97. doi:10.2105/ajph.1.11.783
- Hargrove, Maddy; Hargrove, Mic (2006). Freshwater Aquariums for Dummies. Hoboken, New Jersey: Wiley Publishing, Inc. ISBN 9780470051030.
- Land, Brenda (April 2005). “Using Vitamin C to Neutralize Chlorine in Water Systems.” Recreation Management Tech Tips. U.S. Department of Agriculture Forest Service Technology and Development Program.
- Lawrence, Stephen A. (2004). Amines: Synthesis, Properties and Applications. Cambridge University Press. ISBN 9780521782845.
- Potwora, R. J. (2009) “Chlorine and Chloramine Removal With Activated Carbon.” Water Conditioning and Purification Magazine.
- U.S. Environmental Protection Agency (EPA). “Chloramines in Drinking Water.” Drinking Water Requirements for States and Public Water Systems.