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.
Well, as far as I know, sometimes dry eyes or what you call dehydration, could lead to some uncomfortable feelings, such as painful eyes, watery eyes, bloodshot eyes as well as dry eyes. I mean, if you have got red and bloodshot eyes from time to time, and the situation remains bad, then you perhaps have got dehydration. Of course it is not resulted from simply a lack of water.
There are many causes for red and bloodshots in eyes. Dehydration could be one of them. Usually eye dehydration is caused by tears reduction. Tears are very good for eyes. They are lubricant in eyes, which make our eyeball easy to turn without gritty and uncomfortable feeling. With dehydration, you might feel vision blurred, grittiness and sensitivity to light. You keep feeling there is something in your eyes, but actually not. If you are wearing contact lenses, you might feel very uncomfortable. Drink more water to keep enough water in body. If you have eye drops, take some eye drops would make your eyes better and relieve the uncomfortable feeling.