Distilled water is water that has many of its impurities removed through distillation.
Distillation involves boiling the water and then condensing the steam into a clean container. Where exceptionally high purity water is required, double distilled water is used.
Distilled water is preferable to tap water for use in automotive cooling systems. The minerals and ions typically found in tap water can be corrosive to internal engine components, and can cause a more rapid depletion of the anti-corrosion additives found in most antifreeze formulations.
Distilled water is also preferable to tap water for use in model steam engine boilers and model engines of other types. Mineral build-up resulting from the use of tap water in model boilers can severely reduce the efficiency of the boilers if run for long periods. This build-up is known as boiler scale.
Conductivity is a measure of the ability of water to pass an electrical current. Conductivity in water is affected by the presence of inorganic dissolved solids such as chloride, nitrate, sulfate, and phosphate anions (ions that carry a negative charge) or sodium, magnesium, calcium, iron, and aluminum cations (ions that carry a positive charge).
Electrical conductivity or specific conductance is the reciprocal of electrical resistivity.
Conductivity is measured in micromhos per centimeter (µmhos/cm) or microsiemens per centimeter (µs/cm). Distilled water has a conductivity in the range of 0.5 to 3 µmhos/cm. Industrial waters can range as high as 10,000 µmhos/cm.
The conductivity of water from various sources:
Absolute pure water - 0.055 µS/cm
Distilled water - 0.5 µS/cm
Mountain water - 1.0 µS/cm
Most drinking water sources - 500 to 800 µS/cm
Sea water - 56 mS/cm
Max for potable water - 1055 µS/cm
Electrical conductivity of water samples is used as an indicator of how salt-free, ion-free, or impurity-free the sample is; the purer the water, the lower the conductivity (the higher the resistivity).