This is one of those "split decisions" so common to home wine making. Some folks agree with Tim, others think that adding water weakens the wine significantly. And I guess others are in between.
Personally, if the wine needs just a bit of water, then thats what I do. If it needs a lot of water, then I get a bottle of wine to add. What is a bit and what is a lot? Whatever I feel like, I guess.
If you have a modern Italian carboy, you will find that it is a litre or so larger than 23 litres (or 6 US gallons). That pretty much guarantees that you should be adding wine.
the procrastinating wine maker in the Niagara Region of Ontario Canada
"Visual signs of fermentation are highly overrated"