Distilled Water will be quite shelf stable for dilution of chemicals. There's been times where I found I had to slightly cut and dilute products like Polishes and Compounds, just so thick they'd be a chore just to get out of the bottle. IMO that's just too darn thick!
And sometimes such products are fine when you purchase them, but when used at a later date, this can happen, and they become difficult to use. I say no harm with a very slight dilution to achieve the viscosity it once possessed.
Drinking waters such as you buy in a store, either the coin-op where you fill your own Container, Culligan, and multitudes of others now sold by Bottling Companies are often fully stripped of dissolved solids, heavy metals, and yes even viruses due to the types of filtration and sterilization processes, then a couple minerals are re-added to them. There's Deionization, and Reverse Osmosis.
For the use of dilution for Auto Detailing Products, I would personally give the nod to Distilled Water being more shelf Stable, and having less in the way of dissolved solids versus any Drinking Waters.
Way way back, there was a craze for awhile, people (Health Nuts) were drinking Distilled Water, thinking it was better for them. Nope, it isn't. The body needs those minerals.
Then further up the ladder there are waters that are even further purified. Reagent Grade is one, specs can vary, and they climb still yet higher, for Laboratory, and Scientific Research. Such purified waters are I understand used also in Kidney Dialysis.
And even further, as I've understood from study, some of these very highly purified and stripped waters actually come to the point of being poisonous to the human body.
Water is a very complex study.
