Water is very important. You need 8 to 15 glasses of water per day. Tap water is the same thing as bottled water, it doesn't matter what you drink.
Water lubricates joints
MOST IMPORTANT THING
Water is one of the most important things in your body. Your body is 50-70% water. There is such a thing as too much water as well. You need to be careful to not drink too much, but drinking too little is more of a concern.