Why the water height is held constant in the tank in Reynolds number test?

In a Reynolds number test, maintaining a constant water height in the tank ensures consistent flow conditions and allows for accurate measurement of fluid properties. This stability minimizes variations in hydrostatic pressure, which could affect the flow regime. By keeping the water height constant, the relationship between flow velocity, viscosity, and density can be more reliably assessed, facilitating a clear analysis of laminar versus turbulent flow behaviors.