My daughter moved into her "new" house (older home) about 3 months ago. The previous owner lived there by himself. My daughter has 4 children. So she uses a lot more water. She has a submersible pump. At certain times, her water supply is zero. The guage on the tank says zero. At the well casing, I can hear the pump running. Inside the house, if I turn the main valve off, the pressure begins to rise. After 10-15 minutes the pressure is back up, but if I open the main valve all at once, the pressure goes to zero again and the whole process has to be redone. IF I open the valve slowly and let the system come up to pressure gradually, the pressure drops slightly while the water is going in and then stabilizes. She will then be fine again, until someone flushes the toilet while the washer is filling, doing dishes etc. I am at a loss to figure out the problem. Backflow preventer? Pressure tank air pressure too low?