Drink at least 8 glasses of water every day. Water is life. It is so important and so many diseases and deaths could be avoided simply by drinking more water. A headache is just your body telling you that it needs more water.
Plenty of water is also still the best remedy for hangovers.
To better understand what water really is and get amazed about what Nature has created, read The Hidden Messages in Water from the creative Japanes scientist Masaru Emoto.