A lack of water is bad for your joints. What's cushioning the joints is partially water. When you dehydrate, the water has to come from somewhere.
I found that when I switched from bottles of water to a camelback system I drank a lot more water and felt better over all. One symptom of dehydration is a rapid heartbeat, too.
The salt thing is true, too. If you ever find yourself unable to drink enough to satiate, you might have hyponatremia, which is a lack of salt in your body. Salty snacks instead of sweet does the trick. (Personally, I can't stand anything but plain water.)