Reader question: How do I connect old and new readings when a water meter is replaced, without subtracting meter readings from different devices?
The water meter is replaced and the annual statement comes later. The new reading is much smaller than the previous one. This is initially not a consumption decrease and not a negative consumption: you are seeing numbers from two different devices. For a comprehensible statement, each measurement interval is considered separately and then connected with the appropriate second interval.
All following steps are our own editorial recommendations with fictitious figures. They do not establish any legal billing key, any calibration period or any technical inspection procedure.
Find the four values for the same consumption area
For a complete transition you need the previous starting value of the old device, its reading at removal, the actual starting value of the new device and its later end value. This includes the respective device identifier, date, unit and an unambiguous assignment to the specified consumption area.
In the example it is consistently about the same cold-water consumption of the same flat. Hot water or another flat’s meter are not written into the same sequence of numbers. Record the actually visible unit and decimal places. If the display is unclear, ask for the appropriate reading explanation for that device instead of guessing its meaning.
When changing the meter a copy of the existing work or replacement receipt is helpful. Where safely accessible, your own photos can supplement the assigned old and new reading. Your own photograph does not replace a professional inspection and does not require opening covers or intervening on the device.
Form two differences and only then add
The fictitious annual start of the old device is 320 m³. At removal it shows 328 m³. This first measurement interval gives 328 minus 320, i.e. 8 m³.
The new device is installed with a documented starting reading of 2 m³. At the end of the year it shows 5 m³. The second interval gives 5 minus 2, i.e. 3 m³. For the two intervals fully recorded here together, 8 plus 3, i.e. 11 m³, are reported.
The calculation 5 minus 328 would be an operation between two devices and does not solve the task. Likewise, the assumption that the new device started at zero would in the example produce an additional two cubic metres. Decisive for this calculation is the actually documented starting reading, not a convenient round value.
Request a missing value specifically
Suppose the fictitious replacement receipt is missing the 328 m³ removal reading. The correct enquiry to the responsible body is: Which documented removal reading belongs to the stated old device on the named replacement date? A later photo of the new meter cannot answer this question.
Check existing documents for a genuine contemporaneous value. A memory, an unlabelled photo or a previous year’s average are not silently entered as a reading. If only an estimate exists, it remains marked as such with its source. Whether and how a missing measurement basis may be treated legally or for billing purposes is a separate specialist question. This article does not calculate a substitute value for that.
The correct number can still be on the wrong date
Compare the period of each row with the actual replacement. An inadvertently duplicated assignment of the same day or a wrongly transcribed year can make the compilation incomprehensible, even if the photographed displays are correct. Correct your own transcription errors transparently and retain the original receipt.
If the record must be corrected, name precisely the disputed detail: device, date, reading or unit. The generic message “water is wrong” gives the processing office no concrete point to check.
Reconcile with the later consumption statement
When the annual documents are available, look for the two measurement intervals and their assignment. Were the removal of the old device and the documented start of the new device adopted? Does the stated total refer to the same period as your control calculation? Are any estimates shown together with their basis?
A consumption of 11 m³ does not yet determine a euro amount. Prices, cost components and distribution are additional calculation steps with their own basis. In case of a discrepancy, forward the relevant line together with documents for clarification. The goal is a verifiable numerical connection across the meter change; this does not automatically confirm the technical measurement accuracy or the legal correctness of the entire bill.