The belief that a salt water pool is gentler on the eyes than a traditional pool is common, but it often stems from a misunderstanding of the pool’s chemistry. Many people assume these systems are chlorine-free, which is inaccurate, or that the salt itself causes discomfort. Eye irritation in any swimming environment is not caused by the salt or the chlorine alone, but rather by a chemical imbalance between the water and the human body.
Understanding Salt Water Pool Chemistry
A “salt water pool” is fundamentally a chlorine pool that generates its own sanitizer on-site. This process, called electrolysis, occurs inside a salt chlorine generator. The device contains electrically charged metal plates over which the pool water, containing dissolved sodium chloride, passes. The electric current breaks down the salt molecules to produce chlorine gas, which immediately dissolves to form hypochlorous acid. This acid is the active sanitizing agent responsible for killing bacteria and neutralizing contaminants, just as it is in pools where chlorine is manually added.
The chlorine is produced continuously and in a steady supply. The salt itself does not dissipate, but is continuously recycled in the process, serving only as the source material for the chlorine.
The True Cause of Pool Eye Irritation
The burning sensation in the eyes is rarely caused by the free chlorine used to sanitize the water. The true culprit is a group of chemical compounds called chloramines, also known as combined chlorine. These irritants form when free chlorine reacts with nitrogen and ammonia compounds introduced by swimmers, such as sweat, urine, body oils, and cosmetics. Chloramines are significantly less effective as sanitizers and are the source of discomfort.
The sharp, pungent chemical smell often associated with a “too-chlorinated” pool is actually the smell of chloramines. This odor indicates a high level of contaminants, not an overabundance of fresh chlorine. A second major factor contributing to irritation is an improper pH balance in the pool water.
The human eye has a natural pH level of approximately 7.4, and the ideal range for pool water is generally between 7.2 and 7.8. When the pool water’s pH drifts significantly outside this narrow range, sensitive tissues react, causing stinging and redness. A pH that is too low makes the water acidic, which directly irritates the eye. Conversely, a high pH reduces chlorine effectiveness, accelerating the formation of irritating chloramines.
Salinity and the Osmotic Balance of Tears
The salt level in a salt water pool relates to the concept of osmotic balance. Human tears are naturally saline, and the eye’s comfort depends on the pool water having a similar salinity to minimize osmotic pressure differences.
The average salt water pool operates with a salinity level between 3,000 and 4,000 parts per million (ppm). This concentration is extremely low compared to the ocean, which has a salinity of approximately 35,000 ppm. Importantly, the operating salinity of a salt pool is very close to the natural salinity of human tears.
If the pool water were pure fresh water with zero salinity, osmotic pressure would draw water out of the eye’s cells, leading to irritation and redness. Because the salt pool’s low salinity is nearly isotonic with tears, the osmotic exchange is minimized. This balance is the primary reason many swimmers perceive salt water pools as gentler on the eyes.
Minimizing Irritation and Maintaining Comfort
Pool Maintenance
Minimizing eye irritation depends on maintaining proper water chemistry to prevent chloramine formation and pH imbalance. Pool owners must regularly monitor and adjust the pH level, ideally keeping it within the 7.4 to 7.6 range for optimal swimmer comfort and sanitizer efficiency. Consistent testing of free chlorine levels is also necessary to ensure there is enough sanitizer to destroy contaminants before they can fully form chloramines.
A regular shock treatment involves temporarily raising the free chlorine level. This action effectively breaks down existing chloramines, eliminating the primary irritants and restoring the water’s balance.
Swimmer Actions
For swimmers, personal hygiene plays a significant role in pool comfort. Showering before entering the pool removes body oils, sweat, and cosmetics, which reduces the amount of nitrogenous material available to form irritating chloramines. Wearing snug-fitting swimming goggles is the simplest way to eliminate contact between the eyes and the pool water altogether. If eyes do become irritated, rinsing them immediately with fresh water or a sterile saline solution after exiting the pool can help restore their natural balance.