The combination of electricity and water is widely known to be dangerous. This prompts a natural question: why does ordinary tap water conduct electricity, unlike pure water? The answer lies not in the water molecule itself, but in the various substances dissolved within it. These invisible components transform water from an insulator into a conductor.
Understanding Electrical Conductivity
Electrical conductivity describes a material’s capacity to facilitate the flow of electric current. For electricity to pass through any substance, mobile charge carriers like electrons (in metals) or ions (in liquids) must be present. Materials like copper are excellent conductors because they possess free-moving electrons. Conversely, insulators, such as rubber or glass, do not have these mobile charge carriers, effectively blocking the flow of electricity.
Pure water, chemically represented as H₂O, is considered a very poor conductor of electricity. This is because it primarily consists of neutral molecules and lacks a significant concentration of free ions or electrons. Without these mobile charged particles, pure water cannot efficiently transmit an electric current.
The Dissolved Substances in Tap Water
Tap water is a solution containing various dissolved substances, unlike chemically pure H₂O. These substances originate from natural sources, such as minerals leaching from rocks and soil as water travels through the ground. Water treatment processes also introduce compounds, including chlorine for disinfection, fluoride for dental health, and chemicals like lime for pH adjustment. These dissolved compounds often break down into electrically charged particles called ions.
Many dissolved substances are ionic compounds that separate into positive and negative ions when mixed with water. Common examples of positive ions (cations) found in tap water include calcium (Ca²⁺), magnesium (Mg²⁺), and sodium (Na⁺). Negative ions (anions) frequently present are chloride (Cl⁻), bicarbonate (HCO₃⁻), and sulfate (SO₄²⁻). Substances that produce ions when dissolved in water, making the solution conductive, are known as electrolytes.
How Ions Enable Current Flow
These dissolved ions allow tap water to conduct electricity. When voltage is applied across water containing these ions, the charged particles move. Positive ions (cations) are attracted to the negatively charged electrode, while negative ions (anions) move toward the positively charged electrode. This directed movement of charged ions through the water constitutes the electric current.
Unlike metals where electrons carry the charge, in water, the physical movement of these larger, charged ions facilitates electricity flow. The more ions present, the greater the electrical conductivity. This allows tap water to complete an electrical circuit, unlike pure water which lacks sufficient ions.
Water, Electricity, and Safety
The electrical conductivity of tap water has significant safety implications. Because dissolved minerals and salts make tap water conductive, it poses a shock hazard when it contacts electrical appliances. Even small amounts of these impurities can render water conductive enough to transmit dangerous electrical currents through the human body. Therefore, exercising extreme caution when using electrical devices near any source of tap water is important to prevent electrical accidents.