I am about to transfer my latest brew to my secondary in a few days. It had an OG of 1.070 and about 80 IBU's. I forgot to factor in the amount of beer my hops would absorb and it came in at just 5 gallons. I would like to fill a keg with this and dont mind loosing a few gravity points if I add water. Could I take half a gallon of bottled spring water and boil it for 5 minutes, cool it, add it to my secondary, and rack on top of that?
I dont know if this is a factor but, I will also be dry-hopping this brew. Please let me know if it is ok to do and any opinions/experience you have on the matter.
Cheers.

Primary -
Secondary:
Kegged: Gangnam Style IIPA, Kentucky Breakfast Stout Clone, Oak Aged Robut Porter, Your mom
Upcoming Brew Schedule: Winter Warmer, Cider, APA
PFC, BN Army 