Huh. As in some other distribution / delivery systems, (water) loss = total produced (pumped) - total billed (delivered). There are some other variables other than leakage which would need to be accounted for I'm sure, but I suspect it's all very straightforward and well understood. *shrug*
This being the Philippines means that very straightforward and well understood are oxymoronic. Did you look at the picture I posted ? The dirt floating around in it would suggest to me that blockages could be coming into play.
There are a lot of leaks in the pipes that are "repaired" with inner tube bandages. At some places the pipes run downhill. When the water supply is shut off at night there is no more positive pressure in the pipes. The water in the pipes downhill from the leak(s) causes suction (siphon action) dirt and debris can get sucked into the lines. EDIT the suction or vacuum could be a high as -14.5 PSI or 1 bar.
In the US this is called backflow. The device that stops this is called a backflow prevention device. 1st world countries have these installed at every meter. https://en.wikipedia.org/wiki/Backflow_prevention_device Not here.
Well I did glance at your pictures, but I wouldn't have the first clue as to what it means. I was simply commenting on the general speculation regarding water loss (or leakage) in the municipal water system. Phils may not have sophisticated, 1st world systems in most instances, but I do believe that certain basic, fundamental engineering principles are understood.
I always thought it was a "check valve," which we installed in our house in Dumaguete, but wiki: "Check valve (usually not a legally approved method of backflow prevention)"...
I am reliably informed by a Pretty good UK Plummer, that a Non Return Valve can be simply fitted to the Pipe about 2/3 meters from the Meter
The backflow preventor in the illustration is installed at the fawcett as is used to prevent backflow from the dirty outdoor reservoir back into the house. Here many houses are fed from a reservoir. The illustration does servers to explain my point. Dirt can ingress due to leaks in the pipe. Look at the drawing and imagine a hole in the pipe near the top and another hole close to the bottom. Air, dirt and debris will leak in the top hole and water will flow back to the reservoir. Water will also leak out the bottom hole. Dirt, debris and air will leak in the top hole to replace the water that flowed out the bottom. That's my theory on how dirt gets into the water mains. After a rain storm there are huge puddles along the highway in Bacong and no drainage holes. My suspicion is someone was absent from school the day the "water flows downhill" lesson was taught. I'm pretty sure a backflow preventor and a check valve operate on the same principal. They do the same thing.
