If you live in a traditional one-story home, you probably aren't too amazed how water gets around the house from one sink to another, or from one shower to another, it seems on the surface to be pretty darn easy, even though on a basic level, water still has to travel to that sink, as well as to travel up the pipe in order for it to come out at the spigot, which necessitates some sort of water pressure in order to accomplish all this, but the overall vertical rise is relatively tame throughout. However, for a multi-story apartment or housing complex, the issues of water and water pressure gets a lot more complicated. First off, water follows the law of gravity, so that its natural course is to flow in the same direction as gravity directs to go, which is typically downward. The water to your home usually comes from the city and in order for that order water to reach you; it must be pressurized so as to flow through the city's pipes and into your dwelling. Once there, your home will have to have its own pressurized device and/or pressurized reducing valve in order to create a happy medium between the Pounds per Square Inch (PSI) of not being too low and thereby the water not flowing with enough power throughout the home, or too high, and having thereby too strong of a water flow, which, if too strong for too long, will prematurely age the pipes and could later be the cause of expensive and damaging leakage.
Most of us take it for granted, that water just works throughout our house, and don't really appreciate the value of having water readily available at a pressure that is comfortable to take care of the tasks that water does, such as being used with the toilets, shower, laundry, dishwashing, and watering, until something goes horribly awry. The fact that water flows so readily throughout our homes and works so reliability is a testimony to man's mastery of the science and physics of the operation, because without running water, the conditions within our homes would quickly deteriorate into something being quite intolerable.
Often the city water that we utilized each day resides in a water tower up on a hill, making it easier by the virtue of gravity to distribute the water throughout the town through the piping that lies beneath the ground, as well as reservoirs being used throughout the city to store the water for future usage and/or to be pumped into water towers as needed throughout the day. All of this we take for granted, because the engineering behind it has allowed mankind to move water from place to place seamlessly, and not only that, to distribute the water to individual homes in such a manner, that without even really thinking about it, we are able to control the water at our homes, by merely moving the faucet handle up or down, or left to right, and viola, water flows out, as if by magic.