There have been several threads about hydration - do a search.

This is the pack I wear, on Yellow's recommendation, and it's AMAZING. Two liters of water in that pack weighs me down less than 24 oz on a three bottle waist pack. Literally. It doesn't bounce, barely sloshes, doesn't interfere with hip rotation or arm swing, has separate front pockets for gels and phone/ID, plus a decent sized pocket in the back if you need to strip off a lightweight layer, carry an Epi-Pen, etc.

I've been down with a mild stomach virus plus catching up on yard work, haven't run since Monday. Rode with the club today (short ride, skipped the breakfast we usually do, since OSU/Michigan started at noon [Go Bucks!]. Planning on a long run tomorrow...