i drink 1 gallon of water a day is that ok?

It's fine. It's a lot, but it's fine. Probably nearly twice what you need, because everything else you drink and all the foods you consume that have water content, count toward your daily fluid intake.

Too much water is not healthy, so I wouldn't recommend consuming more than you currently do (unless you are expelling a LOT through sweat and urination), and be sure to spread it throughout the day. Too much in a short period is what can be really harmful.

As long as it takes you like 10 hours to drink it... not 15 minutes

If you are always thirty and you live in cool region then you have very high level of sugar in the blood. Or may be you do long-time workouts every day then it's also ok. If not, and you drink just because they say you need to drink, then you'll in some time will get a problem with your kidneys because you will overload them. Normal amount of water is about 3/5 of gallon.

Over hydration is a thing. The common myth saying you need, what, 9 glasses of water, is completely untrue. Although, it is rare to over hydrate. But you should be OK drinking a gallon

That is excessive and can be unhealthy. People have died from drinking too much water.