Plumbing Questions? Ask a Plumbing Expert.
Welcome to Just Answer, my name is ***** ***** I will do my best to help you with your issue. If my initial response doesn’t answer your question then let me know and we can
continue our conversation.
What you describe sounds like a volume (flow) not a pressure problem. Volume problems are caused by a restriction on the water piping. You get good initial flow because of the built up static pressure but once that depletes the restriction reduces flow. Very hard water by itself can reduce the inside diameter of the piping from mineral deposits and can sometimes cause a significant restriction at some specific point. Also if your main shut off is not a ball valve (lever handle) that (usually gate) valve can fail causing a restriction. Also sediment build up at the piping near the holding tank is another possible culprit.
I have been called away. I'll respond if you have any follow up questions when I return in about an hour.