Under Shot Target Volume (Understatement of the Year)

I under shot my target volume by more than a gallon. My OG is really high, of course. I have let it ferment for about a month and a half now and am contemplating adding water to bring my volume up.

Is there any reason not to do so? Would you?

You should have topped it off before you pitched. If the beer is undrinkable then it cant hurt. Just make sure your water is sanitised.

You should have topped it off immediately when you discovered you overshot your volume. It happens all the time. When you calculate your gravity of your current volume and you then use the dillution tool in beersmith to calculate the gravity after toppiing it off with the amount of water you are missing, you almost always come back to what the original gravity should be. I've topped off when necessary and the beer indeed has turned out fine.

Your beer is exactly stronger by the amount of water you are missing, same if you have to high a volume of water, your beer is exactly weekend by the amount of water you over shot. You can fix that by boiling further to concentrate the wort.

Now, I'd leave it, and drink the stronger beer, and chalk it up to next time.

How's it taste? If you like it as is, bottle it up and call it done.

You can also dilute post-fermentation, but it'd be easy to mess it up.

Thanks team!