Can Swimming Pools Go “Chemical-free”?
Fred Reiff, PE

Sunglasses by a poolPool manufacturers sometimes market their products as being “chemical free.” Chemistry 101 teaches us that claim cannot be true in a literal sense, as all matter–including pool tiles, concrete, plumbing and water–is composed of chemical compounds. But if we assume that the “chemical” of “chemical free” refers to treatment chemicals, such as chlorine and other products added to the water, the question becomes: Can swimming pools go “chemical treatment free”?

First: Control Germs

Little Known Facts about Swimming Pool Sanitizers

Salt water pools use chlorine to destroy germs. Chlorine is released by applying electricity to salt (sodium chloride) in salt water pools. In traditionally chlorinated pools, the chlorine is added as a chlorine-containing compound. Salt pool water may feel “silky” because of the presence of sodium in the water.

Chlorine or bromine-based sanitizers must be used with UV light. UV is effective against germs including chlorine-resistant parasites like Cryptosporidium and Giardia, but it must be used with chlorine or bromine for residual sanitation. UV systems work by circulating pool water past UV lamps, where germs are destroyed. But there is a lag time before which germs added in a distant area of the pool will be exposed to the UV light.

Copper and silver ions have sanitizing properties but by themselves are slow acting and do not provide a reliable residual. Therefore, copper and silver ions should be used in conjunction with chlorine, with which they act synergistically to enhance germ destruction.

Pool water must be sanitized to help control the germs introduced by swimmers. Researchers report that on average each swimmer introduces 0.14 grams of fecal matter to the pool; for children the amount is likely higher. (That little statistic should encourage swimmers to shower before swimming.)

Recreational water illnesses that can be contracted by exposure to even low levels of fecal matter in the water include diarrhea, swimmer’s ear and various skin infections. Swimming in a pool of water without sanitizer is comparable to immersing oneself into a large communal bath tub with the neighbors. Need more be said about the need to treat pool water by sanitizing it?

Pool Sanitizers

Destroying waterborne germs that can make swimmers sick is the goal of swimming pool sanitation. Sanitation can be carried out by adding chemicals or by subjecting pool water to ultra-violet (UV) light. Common sanitizing chemicals include the traditional chlorine-based sanitizers, chlorine generated from salt in saltwater pools, bromine-based sanitizers, copper and silver ions, and ozone gas. The following table provides information on these options.

Common Swimming Pool Sanitizers

Pool Sanitizer Common Name EPA Registered? Form Sanitizing Agent Provides Residual Protection? Sensitive to UV Radiation in Sunlight?1
Stabilized Chlorine2 Trichlor and Dichlor Yes Solid Chlorine Yes No
Unstabilized Chlorine Cal-hypo, Bleach, Chlorine Yes Solid (Cal-hypo); Liquid (Bleach); Gas (Chlorine) Chlorine Yes Yes
Halohydantoins and Sodium Bromide   Yes Solid Bromine Yes Yes
Salt Water Pool Salt pools No Chlorine generated by applying electricity to salt water Chlorine Yes Yes
Ozone Ozone Yes Gas Ozone Very short lived. Yes
Copper and Silver Ions Copper, Silver No Ions from electrolytic erosion of metal Copper- Silver ions Yes, but slow acting. No
UV UV Yes Radiation UV Light No No

All of the sanitizers in the table destroy germs, but only chlorine- and bromine-based sanitizers have staying power, meaning the provision of a reliable fast acting residual that results in continuous, efficient germ control lasting past the time of application. This is of utmost importance because the swimmers themselves introduce an unpredictable load of germs and impurities into the water. When pools are properly maintained—and this includes not only chemical but physical treatment such as filtration—chlorine- and bromine-based sanitizers provide a residual level of protection against the incursion of unwanted substances that can reduce pool water quality and make people sick. That is why many “alternative” pool sanitizers—including ozone, metal ions (minerals) and UV—still require a secondary level of protection, most often provided by chlorine-based sanitizers.

In conclusion, in order to maintain swimming pools as healthful recreational environments, they cannot go completely “chemical treatment free.” To claim otherwise is simply inaccurate.

Fred Reiff, P.E., is a retired official from both the U.S. Public Health Service and the Pan American Health Organization, and lives in the Reno, Nevada area.


1Sanitizers that are sensitive to UV radiation in sunlight lose their effectiveness more rapidly than those that are stabilized.
2Stabilized chlorine is chlorine chemically bonded to cyanuric acid; stabilized chlorine helps preserve chlorine from the destructive effects of UV radiation in sunlight.

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