I suspect it of being merely filtered water with fewer impurities, but I’m not sure. Are there any chemicals in it?
De-ionized water, I would reckon. Scary chemicals go into making DI water, but the product is safe as milk. Honestly.
The same type of compounds that are in automatic dishwasher detergent that cause water to “sheet” rather than bead and leave an evaporation spot when they dry. In the case of cars this allows water to be blown off the vehicle more efficiently at the end drying stage with less water spotting.