Thank you BobPE, as usual you eloquently illutrated my point for me, in many more words than I could have imagined. Now let me provide an additional perspective, from the water utility's point of view.
Water meters are a tool utilized for revenue recovery. You see there is really only one number that really concerns water utilities and that is the total volume of water treated in a given time period. Water meters, as a total number measure about 75% to 85% of the total water recovered in a system. Water meters can be sized utilizing hydraulic equations each and every time. Factor in the cost of that engineering, and the price of the meter installation just went up for the municipality. Now, statistically compare those calculations on say a 100,000 services and you'll find that statistically, they fit within the so called "rule of thumb", but now the municipality has just incurred those engineering costs, necessary or not.
Bob, since I am obviously conversing with an experienced individual in water flow analysis and water systems, I totally agree with your reply, in a theoretical world. But you know full well, as I do, that the meters in any given system if they were 100% accurate, would only account for about 70% to 80% of the total treated water produced at the plant. Leakage, fire fighting, flushing, water breaks account for the remaining water. Every measured unit of water will have a rate attached that accounts for the losses, in addition to other costs.
The Utility you referred to in your example has chosen to hire an experienced and competant engineer to review service applications to determine the appropriate meter for a given service. That's cool, because it is very likely that they have realized a potential cost savings within the context of their established water rates, as you wrote about. In the big picture, did the cost of implemantation of the re-sizing program, complete with retro-fitting of meters on older systems, including engineering costs, really save much money? How long is it going to take for that utility to realize a payback for the cost of the retro fit. Did they even begin retrofitting, or are they merely realizing that there is a potential for additional revenues from this point forward, and therefore the Utility engineer reviews applications?
For every rule of thumb, there are going to be anomalies, just as those you described, but in the big picture, the did the "free" or unaccounted water really make a resounding impact on the utility's overall annual budget once implemented? Or was it a small percentage. I've been there, done that. I know the cost to retrofit systems, old plumbing, etc. I also know that in all cases (my instances only) the cost to implement a program was not worth it in terms of dollars and political fallout. I have managed larger towns and know of very large cities that utilize a flat rate system (no meters) for water utility recovery. They are water hogs, but are happy water hogs. I also have worked with cities and towns that have implemented stringent metering and water conservation programs due to growth and the high cost of treatment.
The bottom line here is that you are correct, with water metering, a "rule of thumb" should never replace sound engineering, but on the other hand one must balance the rationale of undertaking the engineering when the outcome is well within the statistical average. Average residential, average outcome. Complex user, variable flows, compound meter - sized by the utility or developer's engineer. I can also produce reams of data sheets illustrating the smaller meter size relative to commercial/industrial service size. I can also produce several Utility specs where within a flow range and line size, a meter size is prescribed, and it is usually smaller! Those are my observattions, and they will be identical to other communities across North America The utility is satisfied and the customer grumbles about water rates. Nuff said. KRS Services
typically have a 5/8" meter. That not a rule of thumb, but a fact. Most meters fail in favour of the user (reading low) so the type of meter to be used is important. Here are some rules of thumb, which work fine, but are not definitive.