Distilled water is water that has been purified by boiling it into steam and then condensing it back into a liquid. This process removes virtually all dissolved minerals and contaminants. The direct answer to whether it conducts electricity is that it is an extremely poor conductor, but not a perfect insulator. For practical purposes, distilled water is considered non-conductive. This characteristic is due entirely to the scarcity of mobile charged particles within the liquid.
Why Pure Water Does Not Conduct Electricity
Electrical conduction in liquids requires the presence of mobile charged particles, known as ions, to carry the current. The neutral water molecule (\(\text{H}_2\text{O}\)) is held together by strong covalent bonds. Because of this stable structure, the molecule does not readily break apart into charged components.
Theoretically pure water is not completely devoid of ions, as a tiny fraction of molecules spontaneously undergo auto-ionization. This process results in the formation of a hydrogen ion (\(\text{H}^{+}\)) and a hydroxide ion (\(\text{OH}^{-}\)). However, only about one in every 500 million water molecules is ionized at any given moment, making the concentration of these charge carriers extremely low.
This negligible concentration of ions results in very high electrical resistance. The theoretical maximum resistivity of pure water at \(25^\circ\text{C}\) is over 18 million ohm-centimeters (18 \(\text{M}\Omega\cdot\text{cm}\)). This resistance classifies pure \(\text{H}_2\text{O}\) as an insulator because there are simply too few ions to sustain a measurable electrical current.
The Essential Role of Dissolved Impurities
In reality, the distilled water commonly purchased is never perfectly pure, which significantly alters its conductive properties. Any substance that dissolves in water and breaks apart into ions will transform the water from an insulator into a conductor. These substances are referred to as electrolytes.
A major source of conductivity comes from dissolved salts and minerals, such as sodium chloride (\(\text{NaCl}\)) or calcium compounds. When these ionic compounds enter the water, they readily dissociate into free-moving, positively and negatively charged ions, like \(\text{Na}^{+}\) and \(\text{Cl}^{-}\). These ions transport an electrical current through the liquid.
Even the purest distilled water begins to absorb atmospheric carbon dioxide (\(\text{CO}_2\)) immediately upon exposure to air. This dissolved gas reacts with the water to form carbonic acid (\(\text{H}_2\text{CO}_3\)). The acid then dissociates into hydrogen ions (\(\text{H}^{+}\)) and bicarbonate ions (\(\text{HCO}_3^{-}\)). The introduction of these ions, even at trace levels, is enough to substantially increase the water’s conductivity, often within seconds of the container being opened.
Measuring Conductivity in Different Water Types
The ability of water to conduct electricity is measured in units called Siemens per centimeter, often expressed as microsiemens per centimeter (\(\mu\text{S}/\text{cm}\)). This measurement provides a direct comparison of ion concentrations across different water sources. The theoretical limit for ultrapure water, where conductivity is solely due to auto-ionization, is an extremely low \(0.055\ \mu\text{S}/\text{cm}\) at \(25^\circ\text{C}\).
Standard bottled distilled water, due to air exposure and minor container leaching, typically registers a conductivity between \(0.5\) and \(3\ \mu\text{S}/\text{cm}\). This is a measurable increase that demonstrates the effect of minor impurities. Tap water, which contains various dissolved salts and minerals, is dramatically more conductive, generally ranging from \(50\) to \(800\ \mu\text{S}/\text{cm}\).
Seawater, with its high concentration of salt ions, measures around \(55,000\ \mu\text{S}/\text{cm}\). This comparison highlights why tap water and especially salt water pose a much greater electrical safety risk than distilled water. The danger stems from the abundance of conductive ions dissolved within the solution.