Stanley and Dankward,
If water curved this wouldn't be possible. They used water to level the Pyramids, the Roman aqueducts and countless buildings. It's more accurate than a laser.
"A water level works on the principle that a
liquid always seeks its own level, it doesn't matter if the body of water is a bathtub or a lake. As long as there are no outside influences at work (such as the wind or tides), the water at one end of the body of water is the same height as the water at the other end."
HOW TO MAKE A HOMEMADE WATER LEVEL
Water levels have been used for thousands of years. The ancient Egyptians used water levels to build the pyramids, and the Romans used them to construct their aqueducts.
Homemade water level.
A water level is easy and inexpensive to make, making it perfect for leveling a deck or shed foundation, and more accurate than a carpenter’s level over long distances.
A water level can also be used around corners that are out of line of sight, something a laser or builder’s level can’t do.
A water level works on the principle that a liquid always seeks its own level, it doesn’t matter if the body of water is a bathtub or a lake.
As long as there are no outside influences at work (such as the wind or tides), the water at one end of the body of water is the same height as the water at the other end. A water level simply substitutes a plastic tube for the body of water.
Here’s how to make your own water level using nothing more than a length of flexible, plastic tubing (available by the foot at home centers in the plumbing department) and two stakes or dowels. We used 3/8″ I.D. tubing for our water, but sizes of 1/4″ I.D. or larger will work as well.
https://todayshomeowner.com/how-to-make-a-homemade-water-level/