Distilled water is not negatively charged. In its pure form, water is an electrically neutral substance. The confusion often arises from water’s unique molecular properties and its ability to interact strongly with charged particles. Understanding the water molecule and the purification process of distillation clarifies why this common assumption is incorrect.
The Molecular Basis of Neutrality
The water molecule (\(\text{H}_2\text{O}\)) is neutral because it contains an equal number of positive protons and negative electrons. The atoms contribute a total of ten protons and ten electrons. This perfect balance ensures the molecule has a net electrical charge of zero.
Water is a polar molecule, which is often mistaken for having a net charge. Polarity means the electrical charge is distributed unevenly, creating slight positive and negative regions. This occurs because the oxygen atom is significantly more electronegative than the two hydrogen atoms.
Oxygen pulls the shared electrons closer, developing a partial negative charge (\(\delta^-\)), while the hydrogen atoms develop partial positive charges (\(\delta^+\)). The molecule’s bent shape prevents these partial charges from canceling out. This internal charge separation, or dipole moment, is responsible for many of water’s properties, but the molecule as a whole remains electrically neutral.
Defining Distilled Water Purity
Distilled water is created through a purification process that removes nearly all dissolved substances. This involves boiling the water to create steam, which separates from non-volatile impurities, and then condensing the steam back into liquid form. The resulting liquid is highly pure \(\text{H}_2\text{O}\).
The substances removed are typically salts, minerals, and dissolved solids that exist as ions. Ions are atoms or molecules that carry a true positive or negative electrical charge. Removing these charged impurities produces water with an extremely low concentration of charge carriers.
This lack of mobile ions is why distilled water is a very poor conductor of electricity, essentially acting as an insulator. Pure distilled water has a conductivity as low as 0.055 microsiemens per centimeter (\(\mu S/cm\)). This low conductivity confirms the neutral status of the purified substance.
How Water Acquires an Electrical Charge
For water to conduct electricity, it must contain dissolved charged particles called ions. Natural water sources, such as tap water, contain various dissolved minerals like sodium, chloride, calcium, and magnesium. These minerals dissociate, splitting into positively charged cations and negatively charged anions that are free to move.
Tap water typically has a conductivity ranging from 50 to 800 \(\mu S/cm\). This ability to conduct a current is entirely due to these dissolved impurities, which act as mobile charge carriers. The water molecules themselves do not carry the current; they simply provide the medium for the ions to move through.
Even in the purest water, a small amount of self-ionization occurs, where a few water molecules split into hydrogen ions (\(\text{H}^+\)) and hydroxide ions (\(\text{OH}^-\)). The concentration of these ions determines the water’s \(\text{pH}\) level, indicating whether it is acidic or alkaline.
Processes like electrolysis or specialized water ionizers deliberately separate or concentrate these \(\text{H}^+\) and \(\text{OH}^-\) ions to produce water with different \(\text{pH}\) values. When water is referred to as “charged,” it is referencing water that is highly conductive due to dissolved ions or water treated to concentrate acidic or alkaline ions. The charge comes from contaminants or treatment methods, not the fundamental structure of the \(\text{H}_2\text{O}\) molecule.