We are in the northeast on a well. We have had no issues with inside water pressure or running out of water. Recently, On two occasions, we filled a 240 gal inflatable pool from the outside hose. Around the time the pool was totally filled, we tried to run water inside the house. The first time, the bathroom sink upstairs went to just a trickle. The second time, we had more water, but it was definitely at a much, much reduced pressure. We have a submersible pump and a 40 gal or so pressure tank in basement. Does this indicate a problem with the well, the pump, the tank, or something else? We have never had any problems before this, and we have not had any problems since, when using water inside the house for every day use.
Correction: size of tank appears to be 20 gal