The whole drinking 8 gles of water a day deal?

i wake up with puffy eyes every single morning, particularly on my top lids (i don't have sty or anything) and i'm rather perplexed on why it does that. i think part of the problem is the lack of sleep thing, but that i can't really help at the moment, but i do try to get at least 6-7 hours of sleep every evening. (aren't i supposed to get at least 8 at the age of 15?) i think the prime reason might be me not drinking enough water, because i heard if you don't your body retains the water you do give it, resulting in your eyes swelling. if that's true, then how do i measure how much water i drink every day? how much is exactly 'a gl', and i'm physically active so, would i need to increase the standard 8 gles to something more? how much more?