Is it possible to limit water flow this way and how is this effect called? I needed to propose a mechanism to store water and keep water flow at the same level with 100% passive equipment.
Here's what I came up with. If you turn a water reservoir upside down and put in another one, with its end under water, the water doesn't run down, because air can't get inside, and water column is held by low air pressure.

Now, if I add a small hole in the bottom reservoir, h will be low, hence water velocity will be low too.

Flow rate will be the same until the upper reservoir empties, and water level starts decreasing.
Am I right? How is this mechanism called? It seems similar but different to medical drip chamber, but can't google out any confirmaiton, nobody discusses its physics.
ADDED Tested this in real life with plastic and washing liquid bottles. Indeed, the flow rate was gradually decreasing, but the device did keep water from bursting out. The upper bottle just gradually kept letting bubbles of air in.
 A: As @user3823992 points, this does not work: the (excess) pressure of water at the level of the hole is equal to $\rho g h$, where $h$ is the altitude difference between the hole and the free surface in contact with atmosphere. As water flows out, $h$ decreases and thus the pressure and flow rate too.
In the tube now, the pressure in the water column is less than the atmospheric pressure, and as the reservoir empties, will get lower and lower, making it harder and harder to maintain the tube in position. Eventually, the water level $h$ will be lower than the tube inlet, and air will flow into the tube, then you'll get a sudden burst in the outflow.
A: I would say that it depends what your requirements are. If you just need approximately a constant flow rate your design is not bad. You can separate the functions of maintaining the level water level and supplying air. You could even totally separate reservoir from the basin and connect it by tubes.
If you need a simple and cheap design, give it some more thoughts!

