I wouldn't personally. Did YOU take a hydrometer reading before YOU pitched YOUR yeast? (friend, yeah right)
If you hit your numbers then I would rather have 4 gallons of good beer than 5 of watery....or if you didn't take a hydro reading, then you will simply have 4 gallons of stronger beer.
If you add water at this stage, you are opening yourself to several possible problems, such as contamination, and/or oxygenation.
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Revvy's one of the cool reverends. He has a Harley and a t-shirt that says on the back "If you can read this, the bitch was Raptured. - Madman
I gotta tell ya, just between us girls, that Revvy is HOT. Very tall, gorgeous grey hair and a terrific smile. He's very good looking in person, with a charismatic personality... he drives like a ****ing maniac! - YooperBrew