Related: how milliq water systems produce pure, laboratory grade water
Summary
Ultrapure, DI water, RO, distilled water, and double distilled quick comparison. I’ve personally worked with Ultrapure, DI-water, and distilled water.
Water purity comparison (source)
MilliQ water (de-ionized water) will leach metal ions from equipment, and will cause the metal to corrode much quicker.
For things like waterbaths and incubators, use autoclaved tap water or autoclaved Type 2 water.
On reddit someone mentioned having used 50/50 of tap water and DI water without any issue.