the answer is "it depends"
it depends on what ratio you plan to mix at and also what type of VG you are using.
Pure VG is very thick and sticky, most of what is sold as VG is actually "AG" (Aqueous Glycerine) and has water added to it already.
There is no such thing as 100% VG liquid (unless you vape pure unadulterated VG) very high VG mixes for allergy reasons, or cloud chasing reasons made with VG and not AG will need thinning out with water or it just won't wick.
60/40 PG/VG or 50/50 work very well without needing any water.
PG carries flavour better because it's thinner and wicks more easily. You'll find that in weather like we have now (hot) liquid also wicks better (as it's warmer to start with)
If you're not one of the 2% of the population that's allergic to PG then go with 50/50 and don't worry about adding water.