This can be compounded if the overall water level in the well varies since the water in the well above the pump serves as a store of water that can be pumped out without needing to be immediately replenished.
Well pump water pressure varies.
Unless you have a well and pump your household water pressure should remain constant but it may vary considerably when appliances showers sprinklers or other water using devices are engaged.
If you think your hot water piping is clogged see clogged supply pipes hot water.
If the plumbing system in your home or the mains pipes supplying your home are many decades old chances are they may be clogged constricted and filled with debris.
It is normal for building water pressure to vary between 20 40 psi or 30 50 psi depending on how your pump pressure control switch is set.
Basic well pump water pressure guide if you live in a highly populated area your water pressure is controlled by the municipal water system and is usually around 60 psi pounds per square inch.
If your water is provided by a private well and the pressure or flow seem to vary or start and stop when you lose water pressure or lose all water supply for some time period but water pressure later returns or improves check the possible explanations outlined just below.