An oz for each lb you weigh

8 cups of water is plenty for me. I am well-hydrated. What is the purpose of drinking so much extra?

One of my turbokick instructors told us you should drink your weight in water oz plus 8 oz for every 30 min of elevated heart rate. I thought it was a great idea. I already drink more than this but so many people say "8 cups a day" and that just doesn't seem like it should be enough for anyone.

Drink half your weight in water is how I have been educated and the rule that I follow.

I was told HALF your weight in water. I tend to drink more than that now, but it is definitely a good baseline.

I just drink water when I'm thirsty and until my urine is light colored or clear. (Hope that's not too gross.)

8 glasses is just a rough minimum that's safe to tell the general population most of the time. You have to adjust it for your body mass, the cold or heat and activity level. You also have to adjust for coffee or other diuretics and sodium. There are probably other things I'm missing. Way to complex for me. I just let my body tell me how much.

I just drink water when I'm thirsty and until my urine is light colored or clear. (Hope that's not too gross.)

8 glasses is just a rough minimum that's safe to tell the general population most of the time. You have to adjust it for your body mass, the cold or heat and activity level. You also have to adjust for coffee or other diuretics and sodium. There are probably other things I'm missing. Way to complex for me. I just let my body tell me how much.

That's all you need to worry about.

Right now I drink 2 gallons a day. But I think that works for me. It keeps me from eating a ton and I rarely ever get sick.

That's good that it works for you. I also drink a lot of water. But that doesn't mean it works for everyone, nor does it mean that everyone else has it wrong. We all have different diets, activity levels and other factors that play into this.
Too much water can also cause problems. A friend of mine, who is a trainer in a gym, ended up making herself sick because she was eating a diet low in sodium and drinking tons of water. She wasn't doing it intentionally, but she messed with her electrolytes.

I agree with the guideline someone gave above by using urine as a measure.

Maybe the only other thing to worry about is if you can't ever get enough to drink. If it's winter and you're sedentary and always thirsty and drinking massive amounts of water (i.e. a gallon or so) get checked out by your Dr. ASAP.

I don't believe the opposite is true. It's common for people to not crave precisely what they need and to often be mildly dehydrated- hence the guidance. Your body doesn't need absolute precision and operates perfectly within a normal range. Most of the time it's better to error on the side on more water rather than less as long as you don't go nuts and mess up your electrolyte balance. I think learning the signs and symptoms of dehydration and electrolyte imbalance are more important than any exact cups per day formula.

You know drinking too much water can cause issues, right? I drink 100-125 oz. a day and that is perfectly fine for me.

Drinking your body weight sounds excessive to me as a regular strategy. I'm 160lbs and would need to drink 1.25 gal/day. If I'm sweating that much from intense training or heat I'd need some Gatorade or something also. My demand for water always pulls back on days when I'm not sweating as much.

Drinking 2gal/day is excessive- even on a high sodium diet and especially on days when you're not working out and sweating a lot. It isn't my experience high protein makes me crave that much more water (i.e. 4x). It is usually dangerous if you are forcing yourself to drink this much. If it comes easily it can be a sign of diabetes or an endocrine problem and needs to be checked out. I might be way off the mark here & really hope you already have a clean bill of heath - but it just doesn't sound right to me.

water toxicity waiting to happen?

Just sayin~