There are many things that can effect how corrosive the water is to copper pipes, not just the pH. There may be improper grounding of the electrical service causing electrolytic dissolution of copper or a small appliance improperly grounded to the plumbing. If it is the water quality there is something called the “Langelier Saturation Index” that might help you to figure out what is causing your copper pipes to corrode. It is a formula that determines weather your water is neutral, scale forming or corrosive. You need to know temperature, pH, Total Dissolved Solids (TDS), Alkalinity, calcium carbonate etc. Carbon Dioxide causes corrosion in copper. Water softer than 50 mg/l CaCO3 is corrosive. There can be many other reasons. I always like to start with a complete water analysis.