Distilled water is used for industrial and scientific purposes.
Laboratory applications and testing in order to achieve an accurate result in experiments. Distilled water is often used as it does not contain any minerals or contaminants that may affect the experiments outcome.
Automotive uses eg. lead-acid batteries and cooling systems. Tap water contains minerals that is corrosive to the metal components found in the engine. Since distilled water is clear of these particles, it is safe to use in cooling down engines and cleaning.
Using distilled water in humidifiers prevents mineral build up, allowing the humidifier to work better and last longer.