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Legionella Testing: Landlord Duties in Germany 2026

Last updated: 16 October 2026 · Reading time approx. 9 minutes

Central hot water, ten tenancies, a shower in every flat — that makes legionella testing not a recommendation but a duty backed by fines. Look it up online and you will find contradictory answers (annually or every three years?) and a technical term the ordinance does not use at all. This article goes to the ordinance itself: who is caught by the duty, who is not, how often you have to test, what to do once you get a positive result — and which part of the cost actually ends up with the tenant.

Three conditions, and all three have to coincide

The testing duty sits in § 31 (1) of the German Drinking Water Ordinance (Trinkwasserverordnung, TrinkwV). It applies to the operator of a building water supply installation where the drinking water is supplied "in the course of a commercial or public activity" — and then only if three conditions are met together. If one of them falls away, there is no duty to carry out a systemic test.

ConditionBenchmarkTypical case
Size of the installation A storage or central instantaneous water heater with a content of more than 400 litres — or more than 3 litres in at least one pipe between the heater outlet and the tap (the circulation pipe does not count) Central hot water in the basement with long risers; the 3-litre criterion bites even with a small tank
Aerosol formation Showers or other installations in which the drinking water is nebulised Virtually every flat — legionella are inhaled, not swallowed
Type of building The installation is not located in a one- or two-family house Apartment buildings from three units upwards

Letting is itself the "commercial activity": § 2 no. 8 names it expressly, and no taxable profit has to be established. It is not a public activity, though — under § 2 no. 9 that means supplying an indeterminate, changing group of people, which tenants known by name are not. This distinction decides two things: the testing interval and the notification duty.

The term "Großanlage" does not appear in the statute. Many guides speak of a "large drinking water heating installation". In the full text of the Drinking Water Ordinance as amended on 24 June 2023 — 70 pages — the word does not occur once; what counts are the two thresholds above. Searching for it therefore tends to land you on texts describing the position before the recast.

One- and two-family houses are exempt — let or not

This is the clearest and most frequently overlooked relief: § 31 (1) no. 3 excludes installations located in a one- or two-family house — regardless of whether the property is let and how large the tank is. A let two-family house with a 500-litre tank and showers in both flats triggers no testing duty; only the third residential unit brings the building within scope. It does not release you under tenancy law, though: under § 535 (1) BGB the leased property must be kept "in a condition suitable for the contractually agreed use", and sound drinking water is part of that.

Every three years — annually only for a public activity

This is where older guides get it wrong. § 31 (2) no. 2 distinguishes by the type of supply, not by the size of the installation:

SituationIntervalProvision
Residential letting (commercial, not public)at least every three years§ 31 (2) no. 2 (a)
Public activity (hotel, sports facility, care home)at least once a year§ 31 (2) no. 2 (b)
Annual case, three consecutive years without findings, installation unchanged and compliantthe public health office may extend to up to three years§ 31 (3)
Newly commissioned installationfirst test 3 to 12 months after commissioning§ 31 (4)

So the ordinary apartment building runs on a three-year cycle. The extension under paragraph 3 is for the public health office to grant, not the owner, and it is ruled out for care homes. The word "at least" matters: three years is the maximum gap, not a date you may push back by six months.

Who may test — and what stays on file for ten years

Under § 39 (1), both the analysis and the sampling may only be carried out by an approved testing laboratory, and the order must cover the sampling as well (paragraph 3) — samples you take yourself are worthless, even if an accredited lab analyses them. The result must be recorded without delay, and the original record must be kept for at least ten years (§ 44 (3)). Two pieces of good news sit alongside that, and both are regularly reported incorrectly:

Independently of that: the water utility's annual information material on drinking water quality has to be passed on to tenants without delay by the connection holder — that is, by the building owner — under § 45 (1).

Once 100 per 100 millilitres is reached

The technical action value for Legionella spec. is 100 per 100 ml under Annex 3 Part II. The wording of § 51 (1) is what matters: the duties bite once the value is reached, not only when it is exceeded. A report showing exactly 100 CFU per 100 ml is already the trigger. Four things then have to happen without delay:

  1. Notify the public health office, unless you have proof the laboratory has already done so — which it is itself obliged to do under § 53 (1). Sitting on a result therefore does not work.
  2. Investigate the cause, including an on-site inspection and a check of whether the installation complies with generally accepted technical standards.
  3. Produce a written risk assessment following the Federal Environment Agency recommendation named in the ordinance.
  4. Carry out the measures required by accepted technical standards — and report them to the public health office (§ 51 (3)).

Tenants must be informed without delay under § 52 (3) once the result of the risk assessment and any usage restrictions and recommendations are available. The measures themselves must be documented immediately on completion and kept available for ten years (§ 51 (4)). A positive result therefore creates a file that has to remain verifiable for a decade.

Which part of the cost ends up with the tenant

That the tenant bears service charges is something the parties have to agree under § 556 (1) BGB. Service charges are only costs that arise "on an ongoing basis" under § 1 (1) BetrKV — the fact that the test is only due every three years does not stand in the way, as the Federal Court of Justice has held for a recurring safety inspection (see below). What follows a positive result has to be kept strictly separate:

ItemCan it be passed on?Basis
Routine test including samplingyes, given a corresponding agreement§ 1 (1) BetrKV; BGH VIII ZR 123/06
Fitting sampling valves (one-off)nonot an ongoing item (§ 1 (1) BetrKV)
Cause investigation, risk assessment, flushing, disinfection, rebuildingno§ 1 (2) BetrKV excludes remedying defects
Administrative effort of organising itno§ 1 (2) BetrKV (management costs)

What is open is where the recoverable part belongs — the Federal Court of Justice has not decided that for legionella testing. Two classifications are defensible, with different allocation keys:

In practice: if you want to recover the cost reliably, name the test under the Drinking Water Ordinance in the lease. Then the allocation holds under either reading. Which items stay with the owner in general is covered in our article on non-recoverable service charges; the deadlines for the statement itself are in our article on the service charge statement.

The tax side is straightforward

Deductible expenses under § 9 (1) EStG are "expenses incurred to acquire, secure and maintain income" — for income from letting and leasing under § 21 (1) EStG that covers both parts, the recoverable one and the non-recoverable one; for the recoverable part the tenant's advance payment is matched by the laboratory invoice, so nothing is left net. A remediation following a positive result is maintenance expenditure and immediately deductible in the year of payment.

In a condominium, the community is responsible

The operator under § 2 no. 3 of the ordinance is the "entrepreneur or other holder of a water supply installation". Where the central hot water installation is part of the common property, the community of apartment owners discharges the duties under § 9a (2) WEG; the test runs through the managing agent and appears in the annual statement. For the letting owner, what remains is to request the evidence for their own records and to classify the share passed on correctly.

What happens if you simply skip it

Failing to carry out the test, or carrying it out late, is an administrative offence under § 72 (1) of the Drinking Water Ordinance — as is failing to keep the record for ten years. § 73 (2) of the Infection Protection Act sets the range: this category is not among those capped at 2,500 €, so it reaches up to 25,000 €. That is a ceiling, not a standard amount.

The second and often bigger risk is a civil one: if a tenant falls ill, the issue is damages and compensation for pain and suffering, and the testing duty is the yardstick. Landlords know the same logic from the duty to keep premises safe in winter: documented proof that you did what was required is worth more in a dispute than the measure itself.

What the courts have decided

Two decisions of the Federal Court of Justice (Bundesgerichtshof, BGH) carry the two questions the ordinance leaves open: who pays for the routine test — and what happens if someone actually falls ill.

BGH, judgment of 14 February 2007 – VIII ZR 123/06

Decided for the inspection of an electrical installation on a four-year cycle — structurally the same case: recurring costs incurred by the landlord for inspecting the operational safety of a technical installation are service charges and can be passed on as "other service charges" "given a corresponding express agreement between the parties to the lease". A multi-year cycle does not conflict with the requirement that costs arise "on an ongoing basis", and the fact that inspection costs indirectly save maintenance does not turn them into costs of remedying a defect. For the landlord that means the allocation stands or falls with the wording of the lease.

BGH, judgment of 6 May 2015 – VIII ZR 161/14

The facts: an oversized hot water system, in places below the required temperature, not serviced for eight years, and a tenant who fell ill and died. The court confirms that contractual and tortious claims for damages and compensation for pain and suffering are available — a breach of the duty to keep premises safe was even conceivable before the statutory testing duty existed. The burden of proof works in the landlord's favour: "The question whether a residential tenant's legionella infection occurred through contaminated water in the rented flat concerns causation establishing liability and therefore requires full proof." For the owner that means service records and temperature logs are the part of the file that counts if liability is ever in issue. The decision's list of provisions still names the earlier version of the ordinance; the testing duty now sits in § 31, which does not change the tenancy law point.

Frequently asked questions

Every flat has its own instantaneous water heater — do I have to test?

Typically not. The first condition in § 31 (1) requires a storage or central instantaneous water heater with more than 400 litres, or more than 3 litres of pipe content between the heater and the tap; decentralised units inside the flat regularly meet neither. What counts is the actual installation, not the number of flats.

Every three years or annually — which applies to my apartment building?

Every three years. Annual testing only applies where the drinking water is supplied in the course of a public activity (§ 31 (2) no. 2); letting to tenants known by name is commercial but not public. Older guides saying "annually, every three years for small installations" reflect a superseded position.

May I take the water samples myself?

No. Under § 39 (1) both the analysis and the sampling may only be carried out by an approved testing laboratory, and under paragraph 3 the order has to include the sampling.

Do I have to report a clean result anywhere?

No — § 44 (2) exempts records of legionella tests from the duty to send a copy. The original still has to be kept, for ten years from the date of the test.

Is the clause "the tenant bears the service charges" enough?

Not for the route via other service charges: there the Federal Court of Justice requires an express agreement (VIII ZR 123/06). Because the classification is not conclusively settled, naming the test expressly in the lease is the only version that holds under either reading.

Testing intervals that remind you themselves

A duty that recurs only every three years is exactly the one you forget. In RenoDiary you set up legionella testing as a maintenance interval per property, file the laboratory report and the record in the Digital Vault, and see the recoverable share directly in your calculation.

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Sources

This article offers general orientation and does not replace individual tax or legal advice within the meaning of § 3 StBerG. Whether a specific installation reaches the thresholds, which interval the competent public health office sets, and whether a lease clause supports the allocation depends on the individual case. The classification of the testing costs in the service charge statement has not been settled by the highest court; the two readings set out above are flagged as such.