In the past, it was common for mechanics to use tap water with their full concentrate antifreeze. However, the science has evolved, and now we like to say that the professional repair technician is a well educated and up to speed on the science of water.
It’s our recommendation, like other antifreeze suppliers in the industry, to always utilize deionized water, or DI water, whenever possible to create your 50/50 mix. If you don’t have any available to you in your shop, using distilled water is your next best bet. The best way to remember: Tap water is ‘Worst’, Distilled water ‘Better’, Deionized water is “Best”.