The Basics: What Happens When You Boil Chlorinated Water?
When you boil tap water, the heat increases the kinetic energy of the molecules. For volatile compounds like free chlorine, this helps them change from a dissolved liquid state to a gaseous state, or off-gas. This process can help reduce the unpleasant taste and odor associated with chlorine.
However, it's crucial to understand that not all water disinfectants are the same. Municipalities can use either free chlorine or, more commonly today, chloramine.
The Difference Between Free Chlorine and Chloramine
- Free Chlorine (Cl₂): This is highly volatile and has a low boiling point. A continuous, rolling boil for 15-20 minutes in an uncovered pot can significantly reduce free chlorine levels. The increased surface area and agitation help accelerate its escape into the air.
- Chloramine (NH₂Cl): A compound of chlorine and ammonia, chloramine is much more stable than free chlorine. It does not easily evaporate and is highly resistant to boiling, meaning this method is ineffective for its removal. Many water utilities have switched to chloramine because it provides a more stable, longer-lasting disinfectant in the pipe system.
The Hidden Risks of Boiling Chlorinated Water
While boiling seems like a simple solution, it introduces several significant risks that make it an incomplete and potentially dangerous purification method.
Concentration of Non-Volatile Contaminants
Boiling removes water through evaporation, but it does not remove non-volatile substances. As the water level decreases, any heavy metals, salts, nitrates, or other dissolved chemical contaminants become more concentrated in the remaining water. This can increase the levels of lead, arsenic, and nitrates to potentially hazardous levels, which can be particularly harmful to infants.
Inhaling Disinfection Byproducts (DBPs)
Heating chlorinated water can release harmful volatile organic compounds known as disinfection byproducts (DBPs), such as trihalomethanes (e.g., chloroform), into the air. In unventilated kitchens, this creates a vapor that can be inhaled. The World Health Organization has raised concerns that long-term exposure to these DBPs, through ingestion or inhalation, may increase cancer risk.
Ineffectiveness Against Stable Contaminants
Beyond the issues with chloramine, boiling is completely ineffective at removing a wide range of other chemicals and contaminants commonly found in tap water, including:
- Pesticides and herbicides
- Lead, mercury, and other heavy metals
- Nitrates
- Fluoride
- Per- and polyfluoroalkyl substances (PFAS)
Safer Alternatives to Boiling Water
For comprehensive water treatment, safer and more reliable alternatives are available that address the full spectrum of potential contaminants, not just biological threats.
Activated Carbon Filters
Activated carbon filters are a popular and effective option for improving water quality. They work by using adsorption to trap chemical impurities, including free chlorine and some DBPs. Filters containing specially treated catalytic carbon are effective at removing the more stable chloramines.
Reverse Osmosis (RO) Systems
Reverse osmosis systems offer the most thorough filtration available for home use. They use a semi-permeable membrane to remove a broad range of contaminants, including most dissolved solids, heavy metals, pesticides, and both chlorine and chloramine. This is considered the best option for those seeking the highest quality drinking water.
Comparison of Water Treatment Methods
| Method | Removes Free Chlorine? | Removes Chloramine? | Removes Heavy Metals? | Creates Byproducts? | Pros | Cons |
|---|---|---|---|---|---|---|
| Boiling | Yes (partial) | No | No | Yes (DBPs) | Kills pathogens; improves taste | Creates DBPs; concentrates contaminants; ineffective for chloramine |
| Activated Carbon Filter | Yes | Yes (catalytic) | No (usually) | No | Effective, simple installation; improves taste and odor | Does not remove all heavy metals or pathogens; requires filter replacement |
| Reverse Osmosis (RO) | Yes | Yes | Yes | No | Most comprehensive removal of contaminants; high quality water | Higher upfront cost; water waste; slower filtration |
Conclusion: Making an Informed Decision
While boiling can kill bacteria and reduce some free chlorine, it is not a safe or comprehensive method for purifying tap water, especially given the widespread use of chloramine and the presence of other chemical contaminants. The act of boiling can unintentionally create and concentrate harmful substances, posing risks that outweigh the benefits. For consistent access to safe and clean drinking water, investing in a certified filtration system like activated carbon or reverse osmosis is the more reliable and responsible choice. Always check your local water quality report to understand the specific disinfectants and contaminants in your supply. For more information on water safety, consult reliable sources like the World Health Organization (WHO) or the Environmental Protection Agency (EPA).
