Someone with more weight re running needs to answer this. Physiologically, I'd say you're absolutely fine re hydration. Again, the body - physiologically - is designed to self regulate. The only real risk is cramping, I would think with lots of water. But, its very, very difficult to over hydrate. Basically, your urine output will increase and if you were to SIGNIFICANTLY overhydrate - you'd dilute your electrolytes (your natural potassium, magnesium and sodium levels) and - yes - you could cause some blood chemistry imbalances - which could, theoretically, result in cariovascular arrythmias. This - I believe - to be signficant for those who are "racing" or training at "high" maximum levels. Of course, "high" level training varies by individual. In short: better hydrated, than de-hydrated. Stick to what you know, and what feels right for YOUR body. I think - for most of us - the risk is greater for dehydration in this weather, than over hydration. But, someone else here with more running experience is free to disagree?? . . .