The belief that chlorine in a swimming pool neutralizes or “kills” urine is a common misunderstanding of pool chemistry. Chlorine’s interaction with organic waste like urine is complex. The substances in urine react with chlorine not to clean the water, but to produce harmful chemical compounds. This process degrades water quality and air safety, showing that pool hygiene extends beyond maintaining proper chlorine levels.
Chlorine Does Not “Kill” Urine
Chlorine primarily functions as a disinfectant, designed to kill living microorganisms like bacteria and viruses. Fresh human urine is generally sterile, so there is nothing for the chlorine to “kill” in the traditional sense. When organic material enters the water, chlorine shifts to an oxidizing role. Oxidation is the chemical process of breaking down non-living contaminants, including sweat, body oils, and components of urine. The chlorine expends itself during oxidation, meaning less is available for killing germs. This diversion makes maintaining proper pool chemistry challenging in highly used pools.
The Chemical Interaction
The primary nitrogen-containing compound in urine is urea. When chlorine, which exists as hypochlorous acid (HOCl) in the water, encounters urea, a chemical reaction begins. This reaction generates toxic compounds known as chloramines. Chloramines are also called “combined chlorine” because they are chlorine molecules chemically bound to nitrogen-containing organic material. The reaction produces a mixture of compounds, including monochloramine, dichloramine, and trichloramine. Trichloramine is a volatile gas that readily escapes the water and enters the air above the pool. Other toxic byproducts, such as cyanogen chloride, are also formed from the reaction between chlorine and uric acid, another component of urine.
Why Chloramines Cause Irritation
The strong odor commonly associated with swimming pools is not the smell of free, working chlorine. That distinct “pool smell” is the smell of volatile chloramines, particularly trichloramine, which is a respiratory and ocular irritant. When these gases accumulate, they cause familiar symptoms like red, irritated eyes and itchy skin. The gases also affect the respiratory system, leading to coughing, nasal irritation, and exacerbating asthma symptoms, especially in indoor pools where the air is trapped. The intensity of the smell and irritation are directly linked to the amount of organic waste, such as urine and sweat, that has reacted with the chlorine. A strong chlorine smell is a sign of a dirty pool with poor water quality, not a well-sanitized one.
Preventing the Reaction in Pools
Mitigating chloramine formation relies on reducing the amount of organic material entering the pool water. A simple practice is requiring swimmers to shower with soap and water before entering the pool. This removes sweat, cosmetics, lotions, and other organic matter that would react with the chlorine. Pool operators must also address existing chloramines by periodically performing “shock” treatment, or superchlorination. This involves adding a large dose of chlorine to break the chemical bonds of the combined chlorine compounds. Proper ventilation in indoor pools is necessary to remove volatile chloramine gases from the air, preventing respiratory exposure for swimmers and staff.