Many drink water before they go to be . There are many benefits of drinking water before you sleep. You have to hydrate yourself before you sleep. Because you will be asleep for 6-8 hours and you will probably not be waking up in between to drink a glass of water. So, that means your body is not being hydrated during your sleep.
Our body loses fluids while sleeping. You breathe and sweat (if it is hot) while you are asleep- both which keep reducing your water content in body. And if you have a fever or are a diabetic, your body loses more water than usual during night.
Drinking water before sleeping at night will improve blood circulation. Thus, body will perform cleansing at a cellular level and provides nutrition to the cells and remove toxins from the cells to refresh the body .