It has been known since the time of the Greeks that copper has
special properties that prevent the fouling of drinking water. What
the early Greeks did not understand was it was not the copper
metal, but ions of copper, that kept their water safe to
The idea of using copper and silver ions to keep drinking water
safe for humans was adopted by NASA for the Apollo Project and
subsequent shuttle missions.
Currently, hospitals are using copper and silver metal on door
handles and tables to prevent the spread of disease by surface
contact, as well as in drinking water for patients.
More recently, the idea of using copper and silver ionizers to
prevent the growth of bacteria, fungus and virus in swimming pools
has gained considerable momentum. Let’s look at some of the
science behind how copper and silver work to keep a pool safe and
pleasant to use.
All about ions
Everything on Earth, from the water in our swimming pools to the
base molecules of life itself, is made from tiny particles called
atoms. Every atom is comprised of three things: positively charged
protons, negatively charged electrons and neutrons that have zero
charge. Located at the center of every atom are the protons and
neutrons that together make up the nucleus. Flying around the
nucleus are the electrons.
To understand what an ion is, one must first understand what an
element is: a pure substance made up of only one type of atom. Each
of these atoms has the same number of protons and electrons. For
example, in a pure rod of copper, each atom has 29 protons and 29
electrons. This means that metallic copper is neutral — in
other words, it has a zero charge.
An ion is simply an atom that possesses a charge. To achieve this,
an atom must either gain an electron to form a negative ion (anion)
or lose an electron to form a positive ion (cation). It is the
imbalance between protons and electrons that form ions. For
example, if an atom of copper somehow lost two electrons, it would
have 29 protons and 27 electrons. This would result in an atom that
had 2 more protons than electrons, leading to the formation of a
copper ion with a +2 charge.
How ionizers work
A pool ionizer is simply a device that generates ions by means of a
chemical process called electrolysis — often with little or
Electrolysis is the process of passing electrical current through
metal rods (copper and silver) that are submerged into a solution
— usually water — that contains trace amounts of salts.
The salts employed could be sodium hypochlorite or sodium chloride,
among others. When an electrical current is applied to copper or
silver, the atoms start to absorb electrical energy. Once enough
energy is absorbed, the atoms begin to eject electrons and become
cations. These cations, unlike the metal atoms they are made from,
are soluble in water and will diffuse into the pool, where they
immediately go to work preventing biological pathogens from taking
All living things are composed of proteins, enzymes and DNA
(viruses typically have a similar genetic molecule called RNA). All
of these biological systems are absolutely critical in order for an
organism to function properly. If any one of these systems are
interrupted, the natural functions of the organism will stop
— and if the interruption is serious enough, the organism
It has been demonstrated that copper and silver ions have the
ability to interact in a negative way with the membrane of
pathogens. This negative interaction will cause the cellular
membrane (outer barrier) to become “leaky,” allowing
some of the cellular contents to spill out — a process that
kills the cell.
Another mechanism of action for copper and silver ions is binding
to DNA, or to other large biological molecules such as proteins.
Once this binding has been established, the copper or silver ions
begin to generate radicals that react immediately with the target
biomolecule. The metal ion is capable of repeating this process
again and again, resulting in multiple-hit damage to the same
Copper and silver ions are also believed to disrupt the production
of new enzymes in pathogens.
What ionizers do in a pool
A typical swimming pool uses 2 to 4 parts per million (ppm) of
sodium hypochlorite to keep the water free of pathogen
contamination. If one desires to utilize copper/silver ions to keep
a pool pathogen-free, substantially less chlorine is required. It
has been shown that when used in conjunction with silver and copper
ions, a low concentration of chlorine is actually more effective at
inactivating Legionella pneumophila, the bacteria that causes
The concentrations of copper and silver ions are typically kept
very low for two reasons. The first is that it they are effective
at low concentrations, so it makes little sense to add more if a
higher concentration would not do anything useful for the pool
environment. Second, a standard pool ionizer may add too much
copper to the pool, creating a blue stain. The silver ion
concentration should be maintained at 30-40 parts per billion, and
the chlorine levels should be kept at 0.4 ppm.
It’s interesting to note that the sodium hypochlorite
concentrations required for a copper/silver ion pool are
substantially lower than in a regular swimming pool. It is well
known that if a pool is relying only on sodium hypochlorite for
sanitization, 4 ppm is the industry standard. This drop in the
requirement of sodium hypochlorite has numerous benefits to the
pool owner, including less odor and less skin and eye irritation.
It also greatly reduces the pool owner’s exposure to the
potentially negative health effects of swimming in large
concentrations of sodium hypochlorite — no small concern,
since the byproducts of sodium hypochlorite have been associated
with miscarriages, still births, low testosterone and even
In short, ionization provides many of the benefits of disinfection
while offsetting some of the chemical and environmental concerns
common in traditionally sanitized pools. For customers in search of
a “green” solution to their sanitation needs, this
technology may be refreshing in more ways than one.