@minthybear19 – You're body craves salt to make you thirsty. It's a little confusing to me too, but that's what happens. You would think your body would just make you crave water.
If you're wondering about the eight glasses thing, it's an average. I looked into it because I was trying to lose weight and heard somewhere that you need to drink a lot of water to do so. Honestly, everyone's body is different and has different needs.
On average, a person urinates about six cups of liquid everyday – you're supposed to replace that liquid. Caffeine increases kidney function – so you should drink several cups more. Hope this helps a little.