Hi
@Alcapwn1999 - you may have heard of people using
distilled water in small percentages to thin out vegetable glycerin - this is generally only for people who have a sensitivity to propylene glycol, which is what most of us use as both a thinner and a flavor-carrying agent.
When you say "vape pen" I'm thinking you're probably referring to an eGo battery (about the size of a Sharpie) with a tank of the same size. For something like that, 50/50 on the PG/VG is probably a good place to start, unless you know you're PG-sensitive. In that case I'll wait for someone else to chime in on using distilled water, but I don't think you want 20% - you want to avoid rust forming on your coils, which could lead to the inhalation of all sorts of other nasties.
There are lots of diketone-free flavoring options available, most cater more to the fruity vapers than the cream/dessert types. It's still possible to make most recipes without the "bad" flavors - Flavour Art, for instance, has a whole line of vape-safe flavorings that they've tested free of any of the substances currently on health-minded vapers' watch lists. I'd check out Bull City Vapor or another vendor of your choice for supplies to get started - I like BCV because they have warnings prominently posted on flavors known to contain diketones. Unfortunately it's not a complete list and some baddies slip through without the warnings due to the dishonesty/ineptness of certain flavor extract companies (Flavor West comes to mind).
Hope this helps, and good luck!