In layman terms, the water pressure to your house causes by the water reservoir (the big and high water tank in your housing area usually written with your area name).
This is how it works, the higher the reservoir, the higher the water pressure because the pressure ware push from above. Usually at the average of every 10 feet’s high = 1 bar.
Meaning, if the reservoir is 40 feet’s in the heights, the pressure is around 4 bars.
That is why in a 5 floor apartment, ground floor has the highest pressure while 5th floor pressure are the lowest. And high rise condo usually has a step down controller every few floorson the pipes.
However, some complain that even within same housing area, but have different water pressure. Here is why, if the houses nearest to the reservoir is 4 bars, the houses far away would be 2-3 bars or lesser depending on distance due to the pressure have spread so it's lower down. Same as when no one is using, the water pressure is in the pipes without rules. That is why at midnight, the pressure is higher. But water pressure are water flow rates are two different things. You can have a high water pressure and a slow flowrate at the same time. Water flowrates are based on how many litres you can gets in 1 minute (ℓ/mins). Usually cause by the size of the pipe connected to your house.
Why some water filter lowers the water pressure? If it is an outdoor backwash filter, usually it is overdue to backwash or the timer spoiled. This cause the sediments remains in the filter thus blocked the water to flow through efficiently. If it is a ceramic filter at your sink, it is time to clean it.
Below is the measurement of water pressure:
The bar is defined using the SI unit pascal, namely: 1 bar ≡ 100000 Pa.
1 bar is therefore equal to: 10⁵ Pa (pascal), and 14.5 psi (Pound per Square Inch)