I've never been drunk, but I at least know that a hangover is a dehydration-induced headache, where the dehydration comes from the lots of peeing that drinking alcohol makes you do. How could a large intake of water not be the best cure? Unless you pair it with fast-acting painkillers if you can't wait for your body to rebalance itself?
Remember, guys: the only true cure for anything is to stop doing what's causing it (as long as the condition isn't sufficiently advanced that this doesn't work, in which case all you can do is treat it). In this case, depriving your body of water.