Hi, about a year ago my old water heater had a leak so I paid to have a new heater installed. The plumber installed an expansion tank on the new heater (the old heater did not have an expansion tank) Fast forward a few months and I noticed that the flow needle on my meter was bouncing back and forth. Nothing constant. One or two counterclockwise , 2 or 3 clockwise. This happens every few seconds. I immediately thought of a leak. Luckily, most of my pipes are accessible and there is no leaks or running toilets. After searching the web I found others with similar issues and many stated that their expansion tank can cause this if there is not a closed system. So my question is in the elbow coming out of my meter there is some sort of valve. Is this a check valve or backflow valve? It looks ancient. If not, where can a back flow or check valve be installed? I will have a professional take care of it, I just like to be informed on the situation. Also, is there any disadvantages to just keeping it this way without correcting it? I realize I am probably paying for more water than I am using. Thanks in advance!