How bad for the body is it drink a lot of water?

Perhaps: The answer is enough. Most people do not have problem drinking a little more water than needed but in extreme cases (if you are drinking gallons of water daily) water intoxication can occur since extreme load of water can unbalance your body's electrolytes (sodium, potassium..) . In general, the body can sense your water need. As in nearly almost anything in life, moderation is the best answer.