One thing to caution you on the pre-diabetes is that you have to be pretty far along for it to be noticeable during an eye exam. I talked to my optometrist about it over the summer, and he said in 10 years of practicing, he's only had 1 case where it was apparent that the person had diabetes. So you definitely do not want a case where your eye doctor is the one diagnosing it.
Consider the other symptoms of diebetes- are you fatigued, having blurred vision, having extreme hunger? If you're having more than one symptom, then I would check it out with a dr.
Otherwise, the amount of water you're drinking sounds healthy.