Electrical conductivity in water refers to its ability to carry an electric current. This property varies significantly between different types of water, with tap water typically exhibiting higher conductivity than distilled water. The fundamental difference lies in the presence or absence of dissolved substances, which play a crucial role in enabling electrical flow through a liquid medium.
How Water Conducts Electricity
Pure H₂O molecules are not efficient conductors of electricity. Instead, water’s ability to conduct an electrical current depends on the presence of dissolved charged particles, known as ions. These ions originate from inorganic materials like salts and minerals that break apart in water. When an electrical voltage is applied, positively charged ions (cations) move towards the negative electrode, while negatively charged ions (anions) migrate towards the positive electrode, and this movement constitutes the flow of electric current. The higher the concentration of these mobile ions, the greater the water’s capacity to conduct electricity.
Why Tap Water is Conductive
Tap water contains dissolved substances that contribute to its electrical conductivity, picking up naturally occurring minerals and salts like calcium, magnesium, sodium, chloride, bicarbonate, and sulfate as it travels through the ground and plumbing systems. These dissolved compounds dissociate into positively and negatively charged ions. For instance, common table salt, sodium chloride (NaCl), separates into sodium (Na+) and chloride (Cl-) ions. These free-floating ions act as charge carriers, allowing tap water to conduct electricity. The specific levels of conductivity in tap water vary widely depending on the water source’s geological composition and its treatment processes.
Why Distilled Water is Not Conductive
Distilled water undergoes a purification process that significantly removes dissolved impurities, including the ions responsible for electrical conductivity. This process involves boiling water to create steam, which then cools and condenses back into liquid form, leaving non-volatile impurities like minerals and salts behind. The resulting distilled water is essentially pure H₂O, largely devoid of the dissolved ions needed to carry an electrical charge. This absence of charge carriers makes distilled water a very poor conductor of electricity. While perfectly pure water has extremely low conductivity, even distilled water can absorb trace amounts of carbon dioxide from the air, forming carbonic acid and slightly increasing its conductivity, though this minimal conductivity is still substantially lower than tap water.
Real-World Importance of Water Conductivity
The difference in conductivity between tap and distilled water has several practical implications.
In terms of electrical safety, tap water’s conductivity means it poses a greater risk around electrical devices, as it can easily transmit current if contact is made. Wet skin further reduces the body’s resistance, increasing the danger of electric shock.
Industrially, low-conductivity water, such as distilled or deionized water, is important for specific processes. It is used in car batteries to prevent mineral buildup on battery plates, and in electronics manufacturing to avoid short circuits or corrosion.
Boilers also benefit from low-conductivity water to minimize scale formation, which can reduce efficiency. Monitoring water conductivity is also a standard practice in environmental science to assess water quality, as unusual levels can indicate pollution.