On what grounds do you base your skepticism about thus issue? There is all the necessary scientific literature available to support the following view:
On average, the body of an adult human being contains 60% water. Most of the water in the human body is contained inside our cells.
In fact, our billions of cells must have water to live.
The total amount of water in our body is found in three main locations: within our cells (two-thirds of the water), in the space between our cells and in our blood (one-third of the water). For example, a 70-kg man is made up of about 42L of total water.