Water’s interaction with electricity is dictated by its purity. The common understanding that water conducts electricity is only partially correct, as it fails to distinguish between the various forms of water encountered daily and its chemically pure state. The ability of water to carry an electrical current depends entirely on what is dissolved within it. Pure, laboratory-grade water is an electrical insulator, while common tap water is a conductor.
Defining Electrical Conductivity
Electrical conductivity measures a material’s ability to allow the flow of an electric charge, known as electric current. This flow requires the presence of mobile charged particles. In solid conductors like metals, the charge is carried by freely moving electrons. Materials that allow this flow are classified as conductors.
Conversely, an insulator strongly resists the movement of electric charge, possessing few mobile carriers. In liquids, conduction relies on ions—charged atoms or molecules—that must be dissolved and free to move toward an electrode of the opposite charge.
Pure Water as an Electrical Insulator
Chemically pure water, often referred to as deionized or distilled water, is an extremely poor conductor of electricity, making it an effective insulator. The water molecule (\(\text{H}_2\text{O}\)) is covalently bonded, meaning its atoms share electrons and do not naturally form free-moving charged particles. In its purest state, water lacks the necessary charge carriers to establish a current flow.
Although water molecules undergo auto-ionization, where a tiny fraction dissociates into hydronium (\(\text{H}_3\text{O}^+\)) and hydroxide (\(\text{OH}^-\)) ions, this concentration is minuscule. This extremely low concentration limits the electrical conductivity (near 0.055 microsiemens per centimeter), which is why pure water is functionally classified as an insulator.
How Impurities Transform Water into a Conductor
The water encountered outside of a controlled laboratory setting, such as tap water, river water, or ocean water, is never chemically pure. All natural water sources contain dissolved solids, salts, and minerals collected from the ground and surrounding environment. These substances, known as electrolytes, are the agents that transform water into a conductor.
When these impurities dissolve, they dissociate into mobile, charged ions, such as sodium (\(\text{Na}^+\)), chloride (\(\text{Cl}^-\)), calcium (\(\text{Ca}^{2+}\)), and magnesium (\(\text{Mg}^{2+}\)). It is the movement of these mobile ions within the water that allows for the transport of an electric charge. The concentration of these dissolved ions directly determines the water’s conductivity; more ions mean higher conductivity.
For instance, table salt, or sodium chloride, dramatically increases the water’s ability to carry a current because it separates into highly mobile \(\text{Na}^+\) and \(\text{Cl}^-\) ions. Natural drinking water typically registers a conductivity value hundreds or thousands of times greater than pure water due to its mineral content. This mechanism, known as ionic conduction, fully explains why ordinary water is a conductor, while its pure form is not.
Everyday Situations and Electrical Safety
Because all common water contains dissolved minerals and salts, it must be treated as an electrical conductor in all real-world situations. Tap water, even after treatment, contains various ions that allow it to easily transmit electric current, creating a shock hazard.
For safety purposes, the distinction between pure water and common water is irrelevant, as pure water is nearly impossible to maintain outside of a specialized setting. Practical examples of this hazard include pools and bathtubs, where the presence of even small amounts of dissolved minerals and cleaning chemicals ensures high conductivity.
A spill of a beverage or a leak near an electrical outlet presents a genuine danger because the liquid’s conductivity provides a clear path for electricity. The safety guideline is always to assume that any water outside of a specialized laboratory is conductive and poses a risk of electrical shock.