The simplest way to remove chlorine from tap water is to fill an open container and let it sit for 24 hours to several days, depending on the chlorine level. But that’s just one option. Faster, more reliable methods include carbon filtration, vitamin C treatment, and boiling. The right choice depends on how much water you need, how quickly you need it, and what you’re using it for.
Before you pick a method, there’s one critical detail: you need to know whether your water utility uses chlorine or chloramine. Chloramine, a combination of chlorine and ammonia, is increasingly common and much harder to remove. Many of the easiest methods that work for chlorine do not work for chloramine. Your water utility’s annual quality report will tell you which disinfectant they use.
Letting Water Sit (Evaporation)
Chlorine is a dissolved gas, and it will gradually escape from water left in an open container. At room temperature, a standard pitcher with about 2 parts per million of chlorine (a typical tap water level) takes up to 110 hours, or roughly four and a half days, to become completely chlorine-free. Your water might clear in as little as 24 hours if it starts with a lower chlorine concentration, or it might still have traces after five days.
You can speed this up by increasing the surface area of the water (a wide bowl works faster than a narrow bottle), stirring occasionally, or placing the container in direct sunlight. Warmth and agitation both help chlorine gas escape faster. This method costs nothing and requires no equipment, making it popular for watering houseplants or filling fish tanks when you can plan ahead.
The major limitation: evaporation does not remove chloramine. The CDC confirms that while chlorine will dissipate from standing water over a few days, chloramine stays put.
Boiling
Boiling water drives off chlorine much faster than passive evaporation. A rolling boil for 15 to 20 minutes will remove most free chlorine from a pot of water. The heat accelerates the release of dissolved gas, making this the quickest no-equipment method for small batches.
Like evaporation, boiling is far less effective against chloramine. You would need to boil water for an impractically long time to break down chloramine molecules. If your utility uses chloramine, skip this method and use carbon filtration or chemical treatment instead.
Activated Carbon Filters
Carbon filtration is the most practical method for daily drinking water. Activated carbon works by adsorption: chlorine molecules stick to the surface of the carbon as water passes through. This is the technology inside pitcher filters, faucet-mounted filters, under-sink systems, and refrigerator filters. A quality activated carbon filter removes both chlorine and chloramine, though chloramine requires longer contact time with the carbon, so flow rate matters.
For chloramine removal specifically, look for a catalytic carbon filter rather than standard granular activated carbon. Catalytic carbon is processed at higher temperatures and breaks down chloramine more effectively. Many pitcher-style filters use standard carbon and may reduce but not fully eliminate chloramine.
Carbon filters also improve taste and reduce other common contaminants like some pesticides and industrial solvents. They do need regular replacement, typically every two to six months depending on the model and your water usage.
Vitamin C Treatment
Ascorbic acid (vitamin C) neutralizes chlorine almost instantly on contact, converting it to a harmless chloride compound. According to the USDA Forest Service, one gram of ascorbic acid neutralizes 1 milligram per liter of chlorine in 100 gallons of water. Roughly 2.5 parts of ascorbic acid are needed for every 1 part of chlorine.
For a typical gallon of tap water with 1 to 2 ppm chlorine, a tiny pinch of ascorbic acid powder is more than enough. You can buy food-grade ascorbic acid in bulk for very little. Sodium ascorbate, a buffered form of vitamin C, works similarly at a ratio of about 2.8 parts per 1 part chlorine, and it won’t lower the water’s pH the way pure ascorbic acid can.
This method is popular with home brewers, people filling garden beds with treated water, and anyone who needs a fast, chemical-free solution. Vitamin C also neutralizes chloramine, making it one of the few simple treatments that handles both disinfectants. Some showerhead filters use vitamin C cartridges for exactly this reason.
Shower and Whole-House Filters
If you want chlorine-free water for bathing, a showerhead filter is the easiest upgrade. Two common filter media are used in shower filters: activated carbon and a copper-zinc alloy known as KDF-55. The copper-zinc media works through an electrochemical reaction that converts dissolved chlorine into water-soluble chloride ions. Lab testing shows this media achieves 99% free chlorine removal.
KDF-55 has an advantage in hot water because activated carbon becomes less effective at higher temperatures. Many shower filters combine both media. Cartridges typically last two to three months with daily use.
For whole-house treatment, a point-of-entry carbon filter installed where the main water line enters your home removes chlorine from every tap, shower, and appliance. These systems use larger carbon beds and handle higher flow rates. They require professional installation and periodic media replacement, but they eliminate the need for individual filters at each fixture.
Removing Chlorine for Fish and Aquariums
Chlorine and chloramine are both toxic to fish, even at the low levels considered safe for human drinking water. The EPA allows up to 4 mg/L of chlorine in tap water, a concentration that can kill aquarium fish within hours.
The standard aquarium solution is sodium thiosulfate, the active ingredient in most water conditioners sold at pet stores. A homemade version can be prepared by dissolving 32 grams of sodium thiosulfate in one cup of water. Two drops of this solution per gallon of water neutralizes chlorine almost immediately. For extra safety (especially if chloramine is present), using five times the standard dose, about ten drops per gallon, is widely recommended and completely safe for fish.
If you prefer not to use chemicals, filling a bucket and aerating it with an aquarium air pump overnight will remove free chlorine effectively. But again, this does not work for chloramine. If your tap water contains chloramine, a water conditioner or a carbon filter rated for chloramine removal is essential before adding water to your tank.
Reverse Osmosis
Reverse osmosis (RO) systems push water through a membrane with extremely small pores, removing the vast majority of dissolved contaminants. However, RO membranes are actually vulnerable to chlorine. Most polyamide RO membranes tolerate only about 0.1 ppm of chlorine before the membrane begins to degrade. Prolonged exposure enlarges the membrane’s pores and eventually destroys its filtering ability.
For this reason, nearly all residential RO systems include a carbon pre-filter that removes chlorine before the water reaches the membrane. The carbon stage handles chlorine removal, and the RO membrane handles everything else: heavy metals, dissolved salts, fluoride, and other contaminants that carbon alone cannot catch. If you already have an RO system under your sink, chlorine is being removed as part of the process, but the carbon pre-filter is the component doing that work and needs to be replaced on schedule to protect the membrane.
UV Light
Ultraviolet light can break down both chlorine and chloramine, but it requires specific equipment. Medium-pressure UV lamps that emit a broad spectrum between 200 and 320 nanometers are effective for this purpose. The required dose for breaking down chloramine is around 60 millijoules per square centimeter, which is significantly higher than the dose used for basic UV disinfection.
UV dechlorination systems are used primarily in commercial and municipal settings, such as swimming pools and water treatment plants. Residential UV units designed for home disinfection typically use low-pressure lamps at lower doses and are not optimized for chlorine removal. For home use, carbon filtration or vitamin C treatment will be simpler, cheaper, and more effective.
Quick Comparison by Situation
- Daily drinking water: A carbon pitcher filter or faucet-mount filter is the most convenient option. Choose catalytic carbon if your utility uses chloramine.
- Cooking or coffee: A small countertop carbon filter or a pinch of vitamin C powder in a filled pitcher works well.
- Bathing: A KDF-55 or carbon showerhead filter removes chlorine without affecting water pressure significantly.
- Aquariums: Sodium thiosulfate water conditioner provides instant, reliable dechlorination. Use it at five times the label dose for chloramine.
- Garden watering: Fill a bucket or watering can and let it sit uncovered for 24 to 48 hours. For larger volumes, a garden hose carbon filter is available.
- Whole house: A point-of-entry carbon filtration system treats all water before it reaches your plumbing.