The volume of water is as good as the shape of the reservoir (container) it’s in. Often, the containers have a circular, rectangular or a square cross-section.
Water In a Cylinder
Assuming the water is full, then;
If the water is only halfway high in the container, then you’ll need to use half the height of the cylinder in the formula.
Water In a Box Shaped Container
For a rectangular based container, we use the formula to calculate the volume of a rectangular prism also known as cuboid.
For a cube shaped container, we use the formula to calculate the volume of a cube.
Therefore, the volume of water or any other liquid for that matter, is calculated by finding the volume of the container holding the liquid.