Use of an uncalibrated water meter is prohibited: Administrative Court of Gelsenkirchen quashes water notice for €41,900.

Municipalities may not use water meters without valid calibration to issue billing notices for water consumption.When it comes to municipal billing notices for water consumption, the water meter is the cornerstone of every settlement. But what happens when the measuring device has long since ceased to be calibrated? May the municipality use the displayed values nonetheless – perhaps at least as a starting point for an estimate? The Administrative Court of Gelsenkirchen addressed this question in August 2025 (Judgment of 19.08.2025 - 15 K 2823/21) and gave a clear answer: without valid calibration, the meter reading is worthless. Neither a billing nor an estimate may be based on such grounds.

The case: from the horror billing to partial quashing

In the underlying proceedings, a property owner contested a billing notice from his municipality. The water meter on the property had been installed in 2012. According to the applicable measurement and calibration regulations, the calibration period for water meters is six years – it had therefore expired by the end of 2018 at the latest. Nevertheless, the meter continued to be used. In 2019 and 2020, there was also a pipe rupture that caused a significant increase in consumption. On this basis, the municipality set fresh water charges in January 2021 in the amount of approximately €41,900. The owner objected to the demand and argued that the notice was based on meter readings from a device that was no longer calibrated. The city countered that a subsequent condition assessment had shown that the meter functioned correctly from a technical standpoint. For this reason, it was permissible to use the values at least for the purpose of estimating consumption.

The decision: without calibration, no legal basis for using the water meter

The Administrative Court of Gelsenkirchen disagreed. It first made clear that according to § 18 Abs. 1 AVBWasserV, only measuring devices that comply with calibration regulations may be used. Additionally, §§ 31 and 37 MessEG stipulate that uncalibrated devices may simply not be used in commercial operations. These prohibitions also apply in the law of municipal charges, which is linked to the tax code via § 12 KAG NRW. The court was particularly emphatic on the question of whether uncalibrated meter readings might at least serve as a basis for an estimate under § 162 AO. The answer was: No. Whoever uses uncalibrated values for an estimate circumvents the statutory prohibition on use. Accordingly, the estimation results would be as unlawful as the direct adoption of the values.

Condition assessment does not heal the defect

The municipality had relied on a subsequent condition assessment that showed the water meter was measuring within tolerances at the time of inspection. But the court did not accept that either. A condition assessment may indeed make statements about current functionality, but cannot replace a retroactive calibration. The statutory calibration requirement is precisely designed to protect those liable for charges and cannot be circumvented by subsequent investigations.

Estimation only on a permissible basis

In principle, billing authorities may estimate under § 162 AO if no reliable data are available. However, the estimate must be based on a legally sound and economically plausible basis. This may include previous years' consumption or average values from comparable households. Resort to readings from an uncalibrated meter, however, is impermissible. Since the municipality failed to observe these requirements, only a fraction of the claim remained at the end: after the meter was replaced in November 2020, only 53 cubic metres of water could be billed at €1.58 per cubic metre. In addition, there was the annual basic charge. Everything else was unlawful and was quashed.

Consequences for practice

The decision of the Administrative Court of Gelsenkirchen has considerable signalling effect. It makes clear that municipalities are well advised to monitor their calibration periods consistently. Those who fail to replace old water meters in good time risk substantial loss of revenue and potentially even administrative law consequences. For under MessEG, the use of uncalibrated devices is an administrative violation that can be punished with substantial fines. For those liable for charges, on the other hand, the judgment offers valuable points of attack. Anyone who receives a high billing notice should by all means have it examined whether the underlying water meter was still validly calibrated during the relevant period. If that is not the case, the chances of successfully challenging the notice are very good.

Our recommendation

For municipalities: Implement comprehensive calibration management. Arrange for timely meter replacement, properly document all procedures, and adapt your regulations so that estimates are based exclusively on permissible grounds. For those liable for charges: Scrutinize high water billing notices carefully. An uncalibrated meter is a massive argument against the lawfulness of the billing. In case of doubt, you should have an objection filed by a lawyer – the chances of a substantial reduction in the claim are good. Conclusion: The judgment of the Administrative Court of Gelsenkirchen demonstrates once again that measurement and calibration law in municipal charges law is not merely a formality but is of central importance. Those who rely on it can successfully defend against high claims. Municipalities, on the other hand, must urgently strengthen their processes if they do not want to risk that substantial revenues are lost. In doing so, the experts in administrative law at AVANTCORE Rechtsanwälte in Stuttgart can provide you with legal support.