Only drink water at room temperature.
When you drink cold water it might cause your muscles to tighten and cause pain. Your body has to work harder to regulate body temperature to a normal level and can damage your digestive system.
In my opinion we all have an optimum level of water we should drink, mine is 3 liters but we are all individuals so yours may be different.
Try not consume water 1-2 hours before going to bed as you probably have to get up in the middle of the night to go to toilet.
If you are thirsty then you are dehydrated, try and drink regular during the day to keep hydrated to your optimum level.
Drink 30-45 minutes before meals to fill you up therefore you will eat less helping you maintain your weight. After your meal wait 30 minutes as this can dilute the acid in your stomach which is needed to digest the food.