19 lbs is probably pushing the high end for a day hike, given that many folks can go on overnights with about 20-25lbs bags. Figure the 3 liters is 6lbs that you aren't going to give up. What did you carry? A trip that short, I'd carry the 10 essentials, maybe a waterproof jacket or vest for added insulation, and water. Probably tip the scales at 11 or 12 lbs.

Another thought: perhaps the weight of the pack isn't the problem, but rather the condition of the hiker. Obviously I can't see how your physical condition is! I would think 19lbs shouldn't be too much a burden normally, though.

My $.02