Why do you lose water pressure while running water from a well?

There is a difference between pressure and flow in hydraulics such as water. If your source is a water tower, like city water, the pressure is constant, or static, however flow depends upon pipe size and other factors. For example, you may be dissatisfied with the flow of your shower but you look out the window to see a truck crash into a fire hydrant. "No fair!", you cry as you envy the neighborhood children getting a more satisfactory bath than you just had, with apologies to the truck driver abused in this example though he also got a better shower. That is, the six inch diameter fire hydrant main line produces considerably more flow than the 3/4 inch line to your house, especially if someone flushes and robs your flow. To specifically address well water pressure concerns, you have to understand that your pressure is artificially created. You rely on a pump for that purpose. As you investigate potential problems with your pump keep in mind that pressure is not the same thing as flow. See the links. BTW: As a concrete guy, I have a personal interest in hydraulic pressure because it has a direct impact upon my preparation of formwork to contain liquid concrete in its desired place until it hardens. The physics are the same as water, but engineers use a caveat in these pressure calculations which defy common sense. The constant of pressure exerted by height (gravity) is not allowing for friction. "Discounting friction" is how they put it. That is, consider the amount of piping in your home. Okay, now consider the same amount for your neighbors and then image how many others share the same source of water, maybe a million people. Now consider the loss by friction, the rubbing of water molecules against all manner and size of piping, before you can turn on the spigot. Friction loss is huge in hydraulics. I have met men who have formed and poured concrete all their lives who call me crazy when I tell them that a one foot wide concrete wall form has the same pressure at the bottom as a three feet wide form, if the height of the wall is the same. Technically they are wrong, but their experience tells them better. "Discounting friction" in pressure calculations is like getting robbed, discounting the threat.