Science & Wellness Desk
The Copper Current
The red metal that quietly kills microbes, the chemical that took over our pools, and what really slips through your skin when you swim.
Touch a brass door handle in an old hotel and you are touching one of the oldest disinfectants humans ever stumbled on. Copper does not need a spray bottle or a scrub brush. It simply sits there, and the bacteria that land on it start to die. That quiet talent has been noticed for thousands of years, forgotten, rediscovered, and is now being sold back to pool owners as the luxury alternative to the sharp, eye-stinging smell of chlorine. This is the story of how we got from copper to chlorine, what chlorine does once it meets your body, and how to swim cleaner whether your budget is a mansion or a backyard.
Poolside, late light, two different ideas of the same afternoon.
How copper kills a microbe
Scientists call it the “contact killing” effect. When a bacterium touches a copper surface, copper ions are released and go to work on the cell from the outside in. They damage the outer membrane so the cell starts leaking, they trigger reactive oxygen molecules that tear at the cell’s proteins and fats, and they break down its genetic material, the deoxyribonucleic acid (DNA). A thesis from the Universidad de Chile tested pure copper against two of the most common food-poisoning and skin-infection bacteria, Escherichia coli and Staphylococcus aureus, and found that both behaved the same way on copper: they died, while stainless steel and other surfaces offered no such effect.1
Chile, the world’s copper heartland, then moved the test into real hospital rooms. At the Hospital del Cobre in Calama, researchers swapped high-touch surfaces in intensive care units for copper or copper alloys and tracked bacteria for 30 weeks. Their averages showed contamination on the copper surfaces fell by roughly 80 to 90 percent compared with ordinary surfaces, and the copper kept working without any reapplication.2
Chlorine has to be poured in again and again. Copper simply keeps doing its job, for as long as the metal is there.
Who used copper first
The Egyptians. The oldest written record usually cited is the Smith Papyrus, an Egyptian medical text whose content is dated by copper researchers to roughly 2600 to 2200 BCE (before the common era), describing copper used to clean wounds. The same account notes that water carried and stored in copper vessels stayed freer of the microbes behind diarrhea, and that the later Ebers Papyrus, around 1500 BCE, expanded copper’s medical uses.3 Egyptian temples and palaces also used copper to distribute water, while ordinary homes relied on clay.4
The Romans. Here is the closest the ancient world came to copper in a pool. Vitruvius, the Roman architect and engineer, instructed bath builders to set three bronze kettles, called ahena, over the furnace: one for hot water, one for lukewarm, and one for cold, stacked so water flowed from one into the next, with pipes carrying the heated water into the bathing pools. He even specified a bronze disc hung on a chain in the sweat-room dome to control the heat.5 That bronze was plumbing and heating equipment, not a planned sanitizer, so it would be an overstatement to say the Romans used copper to disinfect their pools. Their real defense was a constant supply of fresh water, which ran through the cold plunge pool and out to a fountain.5
The very first pools. The Great Bath of Mohenjo-daro, in today’s Pakistan, dates back more than 5,000 years and held around 200,000 liters.6 We found nothing in the record showing it was sanitized with copper.
Separating legend from record
Social media often says “the ancients kept their pools clean with copper.” The documented history is narrower and still fascinating: Egyptians stored and moved water in copper, Greeks and Egyptians used copper compounds on wounds, and Roman bath water was heated in bronze kettles. Deliberate copper sanitizing of swimming water is a modern technology, and the next section explains where it came from.
The switch to chlorine
By the 1800s, large indoor pools existed, but they were expensive and risky. Owners kept them clean by draining and refilling, which was costly and still let disease spread. The turning point came in 1910, when Brown University began experimenting with chlorine to sanitize its swimming pool. Once a cheap chemical could keep a pool safe without constant refilling, pools spread from the elite to the public and then to backyards.6
Chlorine won for honest reasons. A Spanish occupational-health review from the Universidad de Córdoba sums it up: it is the most commonly used disinfectant because it is the most efficient and the least expensive, and preventing waterborne infection is a genuine public-health priority.15 The trade-off showed up later, in what chlorine creates when it meets us.
Copper’s comeback. Copper has now returned to the water through ionization. A low electric current runs between copper and silver electrodes in the pool’s circulation line, releasing a steady trickle of ions that act as a sanitizing treatment, with copper doing most of the work against algae.9
Does what touches your skin enter your body?
Sometimes. Your skin is a barrier, not a wall. Its outer layer, the stratum corneum, is a tightly packed, fatty shield. Small molecules that dissolve easily in fat can diffuse through it and reach the blood vessels underneath, which is exactly why medicated skin patches work. Charged or water-loving molecules mostly bounce off. So the honest answer to “does pool water get into me?” depends entirely on which chemical you mean.
The pool water chemicals that matter
Chlorine itself is mostly a surface irritant. The bigger story is its byproducts. When chlorine reacts with sweat, skin cells, hair, cosmetics and urine in the water, it forms disinfection byproducts. The best known is chloroform, part of a family called trihalomethanes (THMs).13 Another family, haloacetic acids (HAAs), are acids that stay dissolved in the water.15 How much of these you meet depends on the pool: when Barcelona researchers sampled pools across four regions of Spain, trihalomethane levels varied enormously from one pool to the next.14
How much goes in through the skin
This is where the data gets precise, and where it surprised us.
| Chemical | Through skin | Breathed in | Swallowed |
|---|---|---|---|
| Chloroform, recreational swimmer | about 40–45% | about 50–55% | about 0.5% (adults) |
| Chloroform, competitive swimmer | about 34% | about 65% | small |
| Haloacetic acids | about 1% | about 5% | about 94% |
The chloroform figures come from a risk assessment by Denmark’s Environmental Protection Agency (Miljøstyrelsen). It calculated that for children and everyday adult swimmers, breathing and skin contribute nearly equally to the chloroform dose, while swallowing water adds only about half a percent in adults, rising to as much as 10 percent in children who gulp water while playing. The same report notes that the World Health Organization (WHO) scenarios put the skin’s share far higher, at 80 to 90 percent, a figure the Danish authors considered very large.16
The haloacetic acid figures come from a Universidad de Córdoba study with 50 volunteers. Because those acids are polar, meaning water-loving, skin absorption was the smallest route at roughly 1 percent, inhalation of tiny airborne droplets about 5 percent, and accidental swallowing about 94 percent. Children showed higher levels than adults because they swallow more pool water.15
Fat-loving chloroform slips through skin. Water-loving acids mostly enter through the mouth.
What chlorine does inside the body
Short term. The most common complaints are eye irritation, dry and irritated skin, and ear infections. Studies have also found more asthma and respiratory symptoms among swimmers, linked to the chlorine compounds that hang in the air above indoor pools.13
At the cellular level. In 2010, researchers at the Centre for Research in Environmental Epidemiology (CREAL) in Barcelona ran the first study of genotoxicity, meaning damage to genetic material, from pool byproducts. Forty-nine healthy adults swam for 40 minutes in a chlorinated indoor pool. Afterward the team found increases in markers linked to DNA damage and a rise in a lung protein called CC16, a sign that the lung’s protective lining was being stressed. They also identified byproducts never before described in pool or drinking water, and found the pool water was mutagenic at levels similar to tap water.1011 One of the biomarkers that rose has been associated with cancer risk in healthy people.12
The balanced reading. The CREAL scientists themselves stressed that the health benefits of swimming are real, that their results needed to be replicated in other groups, and that the goal is fewer chemicals with disinfection still guaranteed, not abandoning pools.1011 The Danish assessment found the calculated daily chloroform dose for recreational swimmers and children to be roughly 20 times below Denmark’s tolerable daily intake (TDI), while competitive swimmers training around 20 hours a week reached about the same level as that limit.16 Dose depends on time in the water, which is the single biggest lever you control.
The free fix nobody talks about
Byproducts form when chlorine meets organic matter that swimmers bring in. Barcelona’s researchers recommend three habits that cost nothing: shower before getting in, wear a swim cap, and never urinate in the pool.12 Less organic matter means less chloroform to breathe and absorb.
If money is no object
- A natural swimming pool. The concept was developed in Austria and spread to Germany, Switzerland and France. A planted “regeneration zone” of aquatic plants and microorganisms cleans the water instead of chlorine, much like a clear mountain lake. Spain already has about 250, and there are roughly 900 public natural pools across France, Germany, Austria and Switzerland.7 Critics point out they are essentially very large aquariums that need constant care and regular water changes.8 Note that natural pools usually avoid copper entirely, because it would harm the very plants and microbes doing the cleaning.
- A professional in-line copper and silver ionizer. Installed in the filtration line, it releases a steady, controlled dose of ions. Effective ionization in Italian engineering research ran at 0.2 to 0.4 milligrams per liter (mg/L) of copper and 0.02 to 0.04 mg/L of silver.9 Pair it with an ultraviolet (UV) or ozone stage and a much lower chlorine residual.
- Copper surfaces where hands go. Solid copper or brass rails, ladders and door hardware around the pool house put the contact-killing effect to work on dry surfaces, the same way Chilean hospitals do.2
Budget-friendly ways to swim cleaner
- A floating solar copper ionizer. These drift on the surface and release copper ions using a small solar panel, with no wiring. Replacement copper anodes sell for roughly €30 to €50 on European marketplaces, and complete units are often in a similar range.18 Use one to cut chlorine, not to replace it outright.
- Shower, cap, and no peeing. Free, and it attacks the problem at the source.12
- Choose outdoor over indoor when you can. The Córdoba study found airborne byproduct exposure for pool staff was far higher at the indoor pool, because the droplets build up in humid, enclosed air.15
- Shorter sessions, then rinse. Time in the water is the biggest driver of dose.16 A fresh-water rinse afterward clears what is still sitting on your skin.
- Keep the kids from gulping. Children take in far more through swallowing than adults.1516
Before you buy any copper system
“Chlorine-free” claims. Some sellers promise you can stop chlorine completely. Copper is slow and does not break down sweat and body oils the way an oxidizer does, so most pools still need a small chlorine or other oxidizer residual. Many public pools are legally required to keep a minimum chlorine level.17
More is not better. Too much copper can turn blonde hair green, stain plaster, and corrode metal fittings. Excess copper and silver ions can even deposit on other metals and cause localized corrosion.9 Test your water and stay in range. For context, the WHO drinking-water guideline value for copper is 2 mg/L, far above pool ionization levels.
Saltwater is still chlorine. A saltwater pool uses a generator to make chlorine from salt. It can feel gentler, but it still produces chlorine byproducts.
A note from The Cat House Foundation
Clean water should never come at the cost of the people, or the animals, who use it. A share of Cat House proceeds goes toward feeding programs, beach cleanup supplies, and the future Cat House Sanctuary, where we plan to use plant-filtered, low-chemical water features that are safe for wildlife. Pool water is not for pets to drink, and pool chemicals should be locked well away from curious paws. Every subscription helps us build a world that is a little cleaner and a lot kinder.
Endnotes
- Universidad de Chile, thesis, “Efecto biocida del cobre frente a Escherichia coli y Staphylococcus aureus.” repositorio.uchile.cl
- Diario de Cuyo (Argentina), “Más del 90% de las bacterias puede ser eliminado con cobre,” October 31, 2013. diariodecuyo.com.ar
- Reporte Minero (Chile), interview with Michael Schmidt on copper’s antimicrobial history, August 6, 2020. reporteminero.cl
- Mercado (Argentina), “Del barro al plástico: la evolución del transporte de agua en la historia de la humanidad.” mercado.com.ar
- Vitruvius, De architectura, Book V, Chapter 10, “Über die Anlage der Bäder,” German translation Zehn Bücher über Architektur (Baden-Baden, 1959), digitized by Universitätsbibliothek Paderborn (Germany). digital.ub.uni-paderborn.de
- Mr Pool Man (Australia), “A brief history of swimming pools.” mrpoolman.com.au
- Consumer (Fundación Eroski, Spain), “Piscinas naturalizadas, bañarse como en un lago.” consumer.es
- Consumer (Fundación Eroski, Spain), “Piscinas naturalizadas,” Alex Fernández Muerza, July 16, 2007. consumer.es
- Case-history paper on copper–silver ionization and galvanic corrosion (hospital Legionella system and marine vessel). core.ac.uk
- Universitat Autònoma de Barcelona, UAB Divulga, “Nadar en piscinas cubiertas tratadas con cloro puede provocar daño en el ADN,” September 2010. ddd.uab.cat
- Barcelona Institute for Global Health (ISGlobal) / CREAL press release on swimmer genotoxicity study. isglobal.org
- Consumer (Fundación Eroski, Spain), “Efectos en la salud de los desinfectantes de piscinas.” consumer.es
- Billiken (Argentina), “El cloro de las piletas nos protege de enfermedades, pero ¿puede también perjudicarnos?” billiken.lat
- Gaceta Sanitaria (Spain), “Trihalometanos en el agua de piscinas en cuatro zonas de España,” 2010. scielosp.org
- Cardador, Gallego and Montero, Universidad de Córdoba, “Piscinas de uso público: evaluación de la exposición a ácidos haloacéticos,” Seguridad y Medio Ambiente (Fundación MAPFRE), no. 75, December 2013. fundacionmapfre.org
- Miljøstyrelsen (Danish Environmental Protection Agency), Miljøprojekt 1078, “Sundhedsmæssig vurdering af frit og bundet klor og trihalomethaner i bassinvandet i svømmebade,” chapter 3, 2006. mst.dk
- Ecoportal (Argentina), “Cómo se hacen las piscinas ecológicas.” ecoportal.net
- ManoMano (Spain), solar pool ionizer copper anode listings. manomano.es
