I have to say my urine is always rather dark. However if I have a lemon juice and hot water in the morning, I find my urine is much lighter for the rest of the day and I wouldnt say my water intake has increased any. I drink tea mostly and I think the dark urine is just toxins coming out.... frankly I have no idea if that is the case, but its what I like to think... so perhaps light urine means there arent any toxins to come out... hmmm If I'm ever anywhere tropical for a holiday I have to admit my urine is always lighter... more sweating (more toxins coming out??) and probably more water going in....IMHO, drink until your urine is light and clear. That's the best test. If your urine is dark, you're dehydrated (except the morning - it's typical for your urine to be darker in the morning). But, during the day if your urine remains dark, you need to step up your fluid intake.
I do have a reminder set on my outlook to get a glass of water at 10am and at 3pm each day. Sometimes I even drink it!