If you know the amount of water needed every day, that depends on many factors like weight and activity. Our body is 60% water but we lose it all the time with urine and sweating. As to MayoClinic.com, we lose 6.3 cups daily due to urination and 4 cups from sweating, breathing or bowel processes. From the food, you ingest some water, but not too much, like maybe 20% of daily amounts. So, obviously, you need more water.
All experts agree how water amount is crucial for health and good weight, that amount of water is half of our weight in oz water daily. For example, a man of 160 lbs needs 80 oz water daily.
For inactive people, divide weight in half and see how many oz water you need.
If you are active, divide weight by 2/3 and not ½.