at sea level
Water pressure refers to the pressure of water in a system. In a home it will be 30-50 psi typically and this is governed by the municipal pressure or by a well tank.
Saturated steam is gas-phase water in equilibrium with liquid water at the same temperature and pressure. If the temperature is above the saturation point and/or the pressure is below the saturation pressure, the steam is "superheated steam". In either case it is a gas. There are some conventions where saturated steam along with some fraction of liquid water in equilibrium with it is still referred to as steam even if not all of it is gas, as long as at least some of it is gas.
Flushometer type needs at least 30 PSI to operate semi decently 50 PSI or more would be ideal
House water pressure should be around 50-60 psi.
If you are on city water, a large pipe has burst somewhere causing pressure to drop drastically. If you are on a well, a problem has occurred in your pump, or your pressure tank, or the main pipe between well and house. In extremely cold weather pipes from a well can burst. Many well heads (at least in my area) are very inadequately protected.
at sea level
The pressure is greatest at the bottom of the bottle, where the weight of the water above creates the most force. The pressure is least at the top of the bottle, where there is less water above applying force.
The pressure is greatest at the bottom of the bottle, as it is supporting the weight of the water above it. The pressure is least at the top of the bottle, where there is less water above exerting force.
Yes, at least at 1 ATM pressure.
Gravity. Water will always take the path of least resistance, which is sideways. And if there is pressure from the top, Pascal's principle is in affect which states that when pressure is applied to the top of a body of water the resulting affect is pressure on all other sides of the body of water.
This does vary slightly according to the shower, but for a shower without a pump, using a gravity feed, a water pressure of at least 0.1 bar is recommended. If your water pressure is low you will need to install a pumped shower.
It needs at least 38 psi of incoming water.
A rain barrel should be placed at least 2-3 feet off the ground to optimize water flow and pressure.
You need some sort of an instrument. Most of us just use a pressure gauge, although you could do it empirically--you could throw the end of the hose in water, and if bubbles came out you would know the gas pressure is at least as high as the water pressure--which is 15psi since the 15psi atmosphere is pressing down on the water.
You haven't provided enough information, we need to know, at least, the pressure of said pressure cooker, and even then I'm not sure quite if it's possible. If you look up the phase diagram for water, you can see that the melting point goes down with more pressure.
You need at least 50 psi, and if there is a restrictor, remove it.
Because the water is forcing bubbles from you and it is sucking all the air out of your ears which causes the pressure to hurt.