Well, generally speaking, dehydration can cause red and bloodshot eyes. And red and bloodshot eyes can be the signs of dehydration. You should know that it can dry out your eyes, and then make your eyes become red and bloodshot. According to some experts, when your eyes have dehydration, your eyes can also suffer a lot of other symptom, such as the red eyes, and in some cases, it can also lead to bloodshot eyes. So you need to drink more water. And you should know that even if you have drunk water, the symptom can not disappear soon, for it should be a long term. But just keep your body having enough water. If it still exists, I would suggest you go and consult your optometrist.