The Water Level Devices are close-range devices that are typically used as evidence that the horizon is not at eye level. These devices are essentially a form of surveying, in which markers in the foreground are attempted to be aligned with something distant in the background.

These amateur YouTube experiments are typically discarded as meaningful evidence on grounds that professional surveyors admit that the science is always in error.

http://whistleralley.com/surveying/theoerror/

“ As any surveyor should understand, all measurements are in error. We try to minimize error and calculate reasonable tolerances, but error will always be there. Not occasionally; not frequently; always. In the interest of more accurate measurements, we look for better instruments and better procedures. ”

The greater the distance one is trying to align the devices with, the greater the potential error. All devices need to be of superior calibration, leveling, and positioning. And even then, there is potential error.

Water Not Level

Surface Tension

It has been found that the water in these devices are subject to surface tension and capillary action, and that the levels are not actually level.

From Encyclopedia Britannica we see:

Capillary Action

Further, it is apparent that capillary action needs to be taken into account.

Foreign Substances

It is seen that it is also possible for foreign substances, such as from alcohol or dye used in the experiment, to cause misalignment, since the weights of those fluids isn't consistent with the weight of the water.

From a problem on Chegg Study we find a depiction of unknown liquids floating on water:

Susceptible to Large Errors

It is seen that if the alignment of the water is not perfectly level, and that there is a slight imperfection, then a small misalignment in the foreground will create a large result in the background. The below illustration demonstrated the matter.

Essentially, a very small angle misalignment with the line of sight of bodies in the foreground creates a very large angle numerous miles away.

Inconsistent Results

In one water level device the 'leveled line' appears to change significantly in relation to the mountain in the background with different poisons and sequences, despite the line appearing to be leveled.

Non-Level Water Device

A caged water device was built by a member of our forums, which showed that the device is susceptible to error. In the following device it was seen that the liquid did not perfectly align and that water did not find its level.

Horizon Line Height Variable

Additionally, it should be noted that it has been shown that the height of the horizon is susceptible to the atmolayer. On different days the height of the water in the background changed. The following is from a member of our forums: