Yeah, generally speaking the dehydration can cause the bloodshot eyes. As we all know that dehydration can make us eyes feel dry and also dry skin. At daily life, every people have to drink at least one cup of water because every organ need water to keep our body normal. If we are dehydrated, we should drink more water or soft drinks. At the same time, when you notice that you have the bloodshot eyes, you can clear them by drinking more water. And also, you can ask help for the eye drops, which will wet your eyes and help you to clear the bloodshot eyes. All in all, when you feel your eyes are uncomfortable, you should use some drops because you know our eyes are the window where we can see some beautiful thinks in the world. If my advise does not work, you should consult your personal doctor.