Originally Posted by vogtenstein222
It was a BB Weizenbier extract kit. I boiled 2.5g of water for the wort, then added the other (roughly) 2g when it went to fermentation. I watched the gravity and stopped adding water when it hit 1.047 ( rec'd OG of 1.047 - 1.051 if I remember right - I don't have the paper nearby atm) I wound up with a volume of about 4.25g in the fermenter. Wort temp was at about 70*F, ambient at about 68*F.
Just be careful using this method. Generally, it takes some pretty vigorous stirring to fully mix in top water with wort . . . and failing to stir fully can give an inaccurate gravity reading.
The flip side is that every addition and stir step that you do increases your risk of infection or high side oxidation (unless you're fully cooled).
It is QUITE possible to take a gravity reading, then calculate the exact amount of water you need to add to get to a given gravity. Generally speaking, if you are going to shoot for gravity, as opposed to volume, this would be the way to do it.