I remember when we had to keep car batteries topped off with distilled water.
You either bought a gallon of DW, or left a jug of tap water sit for 2-3 weeks, then you had DW.
Not sure if it's the same, but worked for my 67 Falcon.
Letting it sit won't get you distilled water. Not sure what that's about*.
A few drops of bleach will kill bacteria and get you "purified" for drinking, but distillation requires heat and condensation (see the post upthread about stovetop distillation).
* or am I wrong about that and combined with the FL heat it somehow works?