Yishht87:

Unfortunately, equivalent modeling and testing for liquids and gases are not that simple.

Liquids and gases have different fluid properties, which include density, specific volume, specific gravity, viscosity, kinematic viscosity, changes in viscosity with temperature and speed, vapor pressure, surface tension, compressibility, shear resistance, speed of sound, etc.

Reynolds number is the ratio inertial forces / viscous forces in a fluid.
Inertial forces are proportional to shape, velocity and density.
Viscous forces are proportional to absolute viscosity.

All fluids switch the way they react to a disturbing surface at a range of Reynolds number.
In other words, approximately at Re=500,000 (this post has been edited to corrected this value), for an open flow around an airfoil, any fluid suffers a transition between laminar flow (viscous forces are dominant) and turbulent flow (inertial forces are dominant).

The absolute viscosity ratio water/air is 66.
However, the density ratio water/air is 775.

An in-house test of an airfoil may give you close results for moderate angles of attack and velocities, regardless of using water or air, adjusting the velocity of the water stream to obtain a Re number equivalent to air, as explained above.
However, I believe that more rigorous and exact testing would require a stream of air.

With all respect to your statement, and declaring myself an ignorant in aerodynamic tests in water tunnels, I do not know of manufacturers of airplanes testing their machines in the ocean.
Instead, they all use very expensive tests with air.

I would rather travel in a commercial aircraft that has been tested and certified in a wind tunnel!!

Regards!!