Well, yes, drinking water can improve your eyesight. As we know that when you have drunk enough water, it will make your body, even your eyes work well and smooth. Also, it can avoid many eye diseases, such as dry eyes. But on the other hand, by drinking water, it will lead to good function in your eyes, finally having good eyesight. Also, you should know that you can have some exercise with water. A popular way to exercise the eyes is by submerging the face under water, keeping the eyes open, and rolling them around in their sockets. And just make a few circles clockwise, a few counterclockwise, and move the eyes right-left and up-down a few times. Just do it for many times, it can help improve your eyesight.
Actually drinking water will not improve the eyesight. It will make your whole body full of water content which will be good for your health. If you want to improve the eyes sight, you could eat more carrots or food with vitamin A. They could help you improve the eye vision.
Well, it seems that you are planning to improve your vision. So, as far as I know, our vision could not be improved simply by drinking water and eat whatever beneficial. Despite our eyes need plenty of water to stay healthy and moist, however, they only keep them wet and function well. So it is not true. Maybe you need some other ways to improve your vision. Just consult a doctor.