What is the conductivity range of distilled versus tap water?

The electrical conductivity of water depends mainly on the number of dissolved ions present. Distilled and tap water differ drastically in this regard.

• Distilled water: Pure distilled water has extremely low ion concentration. Its conductivity typically falls between 0.05 to 0.5 microsiemens per centimeter (µS/cm). That’s extremely low—almost like an insulator. However, once exposed to air or stored in containers, it can rise slightly to about 1–10 µS/cm due to absorbed impurities or carbon dioxide.
• Tap water: Ordinary tap water contains dissolved minerals like calcium, magnesium, sodium, chloride, and bicarbonate ions, which come from the ground or plumbing systems. Because of these ions, tap water has a much higher conductivity—typically 50 to 500 µS/cm, though it can vary depending on the local water supply and treatment process.
• Comparison: In simple terms, tap water can conduct electricity hundreds to thousands of times better than pure distilled water. This vast difference is why distilled water is used in labs, car batteries, and medical devices—places where electrical interference or mineral buildup must be minimized.

distilled water = very low conductivity; tap water = much higher conductivity. The difference comes entirely from the amount of dissolved ionic material each contains.