NEED HELP REPLACING WATER LINES

Diagnosing a problem has to start from the beginning. You need to access the water tank and trace/follow the lines to the pump. A leak will not allow the pump to develop pressure. From there you need to trace the line coming from the pump to the sink and so forth. Water lines are sometimes behind cabinets, pull the drawers out and look. It is tedious but necessary. I prefer pex tubing and a clamping device with their collars, they will never come loose. You have some city water which is a good sign, be vigilant and look for leaks, inside and out. Other than starting from the basics there are no diagrams out there that I know of that explain how or where they ran their water lines during the build. Also be sure the water pump screen/filter is clean.