Chloramines are much harder to remove from water than free chlorine. Unlike chlorine, which evaporates from an open container in hours, chloramines are chemically stable and require specific treatment methods to break down. The approach you need depends on whether you’re filtering drinking water, protecting fish in an aquarium, or reducing exposure in the shower.
Why Chloramines Don’t Evaporate Like Chlorine
Many people assume they can leave tap water sitting out overnight or boil it briefly to remove disinfectants. That works for free chlorine, but chloramines are a different molecule. Chloramine (NH2Cl) is formed when utilities combine chlorine with ammonia, creating a more stable disinfectant that lasts longer in pipes. Municipalities switched to it specifically because it persists, reducing harmful byproducts like trihalomethanes by 40 to 80 percent compared to chlorine alone.
That stability is exactly what makes chloramines frustrating to remove at home. In one study measuring how long boiling takes to cut disinfectant levels in half, free chlorine reached its half-life in 1.8 hours. Chloramine took 26.6 hours. That means boiling a pot of water for a few minutes does essentially nothing to chloramine levels. Letting water sit in an open pitcher is equally ineffective. If your water utility uses chloramines (and roughly one in five Americans’ water is treated this way), you need an active removal method.
How to Check If Your Water Has Chloramines
Your water utility’s annual Consumer Confidence Report will state whether they use chloramine or free chlorine. You can also call them directly. The EPA allows chloramines up to 4.0 parts per million in drinking water.
If you want to measure levels yourself, you’ll need a test kit that reads both free chlorine and total chlorine. The difference between those two numbers is your combined chlorine, which includes chloramines. A kit that only measures free chlorine will miss chloramines entirely and give you a falsely reassuring result. DPD-based test kits with separate free and total readings are widely available at pool supply and aquarium stores.
Catalytic Carbon Filters for Drinking Water
Standard activated carbon filters (the kind in most pitcher filters and basic faucet attachments) do a reasonable job on free chlorine but struggle with chloramines. The reaction is too slow at normal water flow rates. For chloramine removal, you need catalytic carbon, which is activated carbon that has been processed to speed up the chemical breakdown of chloramines on contact.
Catalytic carbon is available in under-sink filtration systems, countertop units, and whole-house filters. When shopping, look specifically for “chloramine reduction” or “catalytic carbon” on the product label. Standard carbon filters marketed only for “chlorine taste and odor” are not the same thing. NSF/ANSI Standard 42 certifications that specifically list chloramine reduction are the most reliable way to verify a filter’s claims.
Flow rate matters. Catalytic carbon needs sufficient contact time with the water to break down chloramines. Filters designed for whole-house use have larger carbon beds to compensate for higher flow. If you only care about drinking and cooking water, a point-of-use filter under the kitchen sink is more practical and less expensive.
Vitamin C for Showers and Baths
Shower filters face a unique challenge: hot water flows at 2 to 2.5 gallons per minute, giving any filter medium very little contact time. Most carbon-based shower filters remove some free chlorine but have limited effectiveness against chloramines at that flow rate.
Vitamin C (ascorbic acid) neutralizes both chlorine and chloramines almost instantly on contact. It works by chemically reducing the chloramine molecule rather than filtering it mechanically, so contact time is less of an issue. Shower heads with replaceable vitamin C cartridges are the most common format. Some inline filters combine vitamin C with activated carbon for broader filtration.
For baths, you can also drop a vitamin C tablet directly into the water. Roughly 1,000 milligrams of ascorbic acid will neutralize chloramines in a standard bathtub. Crush the tablet and stir it in before getting in. This is a simple, inexpensive option if you don’t want to install a filter.
Making Tap Water Safe for Fish
Chloramines are lethal to fish and other aquatic life at concentrations well below the 4.0 ppm allowed in drinking water. This is the one situation where getting removal exactly right is critical, because even small residual amounts damage gill tissue.
The standard solution is sodium thiosulfate, the active ingredient in most aquarium water conditioners. It reacts with chloramine to produce tiny amounts of harmless byproducts. The key detail: if your conditioner bottle was formulated for free chlorine, you need to use roughly five times the recommended dose to handle chloramines. This higher dose is safe for fish because sodium thiosulfate is a very mild chemical at these concentrations.
You can also make your own conditioner by dissolving 32 grams of sodium thiosulfate in one cup of water. At the standard dose, one teaspoon of this solution treats 50 gallons. For chloramine-treated water, use five teaspoons per 50 gallons, which works out to about 10 drops per gallon. The solution stays effective for roughly two years. When buying commercial conditioners, check that sodium thiosulfate is listed in the ingredients. Some products use other chemicals that may not handle chloramines as effectively.
One important note: sodium thiosulfate breaks the chlorine-ammonia bond in chloramine, which releases a small amount of free ammonia into the water. In a well-established aquarium with a mature biological filter, beneficial bacteria convert this ammonia quickly. In a new tank that hasn’t been cycled, that ammonia spike can be dangerous. If your tank is new, consider using a conditioner that also binds ammonia, or age the water in a separate container with aeration before adding it to the tank.
Whole-House Systems
If you want chloramines removed from every tap, shower, and appliance in your home, a whole-house catalytic carbon filter installed at the main water line is the most comprehensive option. These systems use large tanks of catalytic carbon media, typically requiring replacement or re-bedding every three to five years depending on water usage and chloramine levels.
Whole-house systems are a significant investment, usually ranging from several hundred to over a thousand dollars installed. They also create a slight drop in water pressure depending on the size of the unit relative to your household demand. Oversizing the system slightly helps maintain flow. For most people concerned primarily about drinking water taste or shower exposure, a combination of an under-sink catalytic carbon filter and a vitamin C shower head covers the main contact points at a fraction of the cost.
Methods That Don’t Work Well
A few common approaches that are effective for free chlorine fall short with chloramines. Standard activated carbon pitchers like basic Brita filters reduce chloramine levels only partially, because the water passes through too quickly. Boiling is impractical given the 26-plus-hour half-life. UV light disinfection systems, popular for killing bacteria, do not break down chloramines. Reverse osmosis does remove chloramines, but most RO membranes degrade faster when exposed to them, so these systems typically require a catalytic carbon pre-filter anyway, which is doing the actual chloramine removal.
Distillation works in theory, since you’re boiling water and collecting the steam, but the energy cost and slow output make it impractical for anything beyond small quantities. For most households, catalytic carbon remains the most cost-effective and reliable method.