Monkey Business - stock.adobe.comCross-flows in single-lever mixers can cause water meters to register even when no water is being drawn. Important for landlords: This doesn't necessarily mean a meter is defective or the billing is incorrect, but usually indicates faulty fittings.
Technical cause: What happens with cross-flows in a single-lever mixer?
Single-lever mixers that do not cleanly separate the hot and cold water supply can create so-called cross-flows. This occurs particularly in the following cases:
- Defective mixing valves
- Cheap products with inadequate sealing
- Outdated fitting design
This is how the currents are created:
- For example, if hot water is drawn from a neighboring apartment, the pressure in the hot water network drops.
- If a single-lever mixer is defective and has a leaky separation, cold water will flow into the hot water system.
- This so-called overflow can trigger the water meter – without any water being actively used in the affected apartment.
Typical effects:
- Water meter moves without water being drawn
- The counter rotates even when the taps are closed.
- Even temporary reverse running of the water meter is possible.
Why is the water meter still working?
Important to know: A water meter measures only actual water movement. It:
- It does not generate a water flow itself.
- does not change the flow direction
- It reacts solely to the actual volume flow – regardless of direction.
If the meter is moving even though no tap is open, that's why not on the device, but rather due to cross currents in the installation.
What can landlords do?
Possible actions:
- Commission a plumbing inspectionA specialist company can check whether cross currents are present in the single-lever mixer.
- Replacing defective fittingsModern single-lever mixers with tested backflow prevention usually cost less than 100 euros.
- Save technical documentation: A test report on the fitting and installation will help with tenant inquiries.
- Inform tenantsMeter readings without water consumption do not automatically mean an error in billing.
Conclusion: Small cause, big uncertainty
Cross currents in the single-lever mixer tap can lead to seemingly inexplicable movements at the water meter. However, a defect in the meter is rarely the cause. It is important for landlords to know the cause and to react calmly – especially if tenants suspect an incorrect bill.
Recommendations for landlords
- Respond to any questions in a factual and technically sound manner.
- Have any unusual fittings checked and replaced if necessary.
- When investigating the cause, consider cross-currents – not just the water meter itself.
Author
Quelle: Handbuch der Wärmekostenabrechnung | Frank Peters Minol Messtechnik W. Lehmann GmbH & Co. KG, 2019
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