Should I add water?

Just made my first batch, followed the recipe exactly, or so I thought, but the carboy (five gallons) is only half-full! There should five gallons of liquid in there! So, should I add more water to the mix? Yeast's already in there and everything's set to go... Will have been five hours at 11:45 PM EST. Help much appreciated.

Is it a 5 gallon batch? If so, add water to bring it to 5 gallons.

Well, what is the recipe?

Partial boil? What's the OG reading from the hydrometer and what is the target?

shoot, I didn't take an og reading. but it was definitely a five gallon batch, and judging from it's color, which is quite dark, I would say something's off. the recipe was for a cincinnati pale ale (again, the one at the very beginning of how to brew). fermentation has begun, as far as I can tell. y'all think I should add water now? wait? not at all? thanks.

p.s. the recipe doesn't give a target og (assuming the author decided that was too complicated to explain to a beginner?).

It sounds like a partial boil kit which means it's intended to be "topped off" in the fermentor. 5 gallon kit made with only 2.5 gallons wouldn't taste right. If it were me, I would top off immediately and shake the crap out of it to get it mixed.

do you think that will that harm the fermentation at all? like kill the yeast or something? it's been fermenting since probably about 12 last night I think.

It won't kill the yeast. It may disrupt them for a bit, but you should be fine. It is still early enough that you want O2 in there for the yeast to do their things so oxidation is not a concern. If you wait much longer, it could become a problem...

great, I'm boiling some water now. thanks!

Make sure that water is COOL before you add it, or you will kill the yeast.

Also, if you have a 5 gallon carboy, you can't realistically put 5 gallons of fermenting wort in there. If that's what you are stuck with, I'd recommend topping off to about 4.5 gallons and just enjoying a slighly stronger beer. If you add 5.0 gallons to a 5.0 gallon carboy, about 1/2 a gallon is going to end up spewing through the airlock anyway!