Never heard of this kind of saying before. It can't be true. There are some ridiculous rumors that some mysterious herbs could lighten the eye color. To see whether all these sayings are true or not, you only have to know the formation of eye color. The colors of eyes are determined by more than one gene. So eye color is inherited. Children are more likely to have the same or similar eye color with their parents. It is decided by the sorts and quantitis of pigment of iris. So there is no possibility to lighten the color by just drinking more water. If you do want to change the eye color, you can try the color contact lenses, which are cheap and safe. You can change any color you like as long as there is such color contact lenses on market.
It is hard to say. Actually, there is no evidence showing that there is any connection between drinking water and eye color. But some people found that drinking much water can lighten eye color. They found that drinking more water can make eyes look more bright and clean. They said that's because drinking more water can promote metabolism.