First of all I have a drilled well with an in well pump. My house is manufactured housing with PEX lines. I recently drained the lines to install a new kitchen faucet. I just shut off the breakers for the pump and water heater then opened up the cold faucet to drain. After the job was done I turned the water pump and heater breakers back on, then turned faucet on. Everything seemed good at first then the pressure dropped off. I tried the outdoor spigots and I got normal pressure at first then dropped right off to low stream. I checked all Faucets and showers in the house and same thing, normal pressure and then very low. I checked the pressure tank and it is pumping up to pressure and the valve on top yields no water just air. Spigot at the pressure tank blasts water out when I open it. Problem occurs with hot and cold water. Screens have been removed from all faucets and still problem exists. I recently installed a water softener about 2 weeks ago because of hard water but problem didn't start till I replaced kitchen Faucet. Could it be the pump? Clogged lines? I am stumped!
Rule out the pump.
Attach a hose to the drain tap at the base of the pressure tank. Run the end outside. Open the tap. If the water system behaves normally, (Pump runs constantly, or runs and shuts off in a cycle that gives reasonable flow) then your pump is doing what it is supposed to.
Check the line between pressure tank and cold line supply.
Since it affects nearly everything, it sounds like you have an almost closed tap between the pressure tank and where the hot water tank cold supply line branches off. Most houses have a single tap you can use to turn off the water to the whole house somewhere from.
I say almost closed, because if it drips it will pressurize the line, including any air pockets. I would expect that you would get between a cup and a quart each time you did this, and it would take minutes to recharge.