Legionella Testing: Duties, Intervals and the Drinking-Water Investigation

Legionella testing is a recurring task for many operators of buildings with central hot-water systems and showers. The German Drinking Water Ordinance (Trinkwasserverordnung, TrinkwV) defines exactly when the systematic investigation is required. The operator also needs a sampling plan that represents the installation, a qualified laboratory and a process for acting on a result. An arbitrary sample from a shower head cannot stand in for the prescribed system investigation.

Under § 31 TrinkwV, the operator of a building water supply installation must arrange systematic testing for Legionella spec. when drinking water is supplied as part of a commercial or public activity and all three technical conditions below are met. The rule also addresses mobile and temporary systems, whose intervals are set by the health authority. In a rented or managed property, identify the actual installation operator and allocate access, commissioning and reporting responsibilities before the test is due.
A building with commercial use is therefore not automatically subject to this specific routine test. The actual hot-water configuration and outlets determine whether § 31 applies. Other water-quality duties can still apply even when the regular Legionella test is not triggered.

The schedule belongs to the installation, not just a tenant’s calendar. Note the commissioning and last sampling dates, and reassess the setup after changes in use, pipework or hot-water generation. Additional tests may be necessary to investigate a finding or follow a health authority’s order.

1. Map the heater, circulation, risers and representative outlets. Have hygienically competent personnel select and document suitable sampling points for the whole system.
2. Commission a drinking-water testing body approved under the TrinkwV. Its remit includes sampling, transport and laboratory analysis; agree access and normal operating conditions in advance.
3. Collect system samples at the hot-water outlet from the heater, at the return of the circulation and at representative points in the distribution. The 2025 Federal Environment Agency recommendation requires the risers to be covered by a justified selection.
4. Record the sample locations, time, conditions and results; review the laboratory report and keep the original investigation record for at least ten years.

The systematic sample reflects the distribution system. According to the updated Federal Environment Agency recommendation, an unused outlet is unsuitable for this purpose, and direct sampling at a shower head is not permitted. Flushing or disinfecting the installation shortly before routine sampling would distort normal operating conditions. A qualified sampler follows the applicable procedure; a separate investigation of a local outlet may use a different sampling purpose.

The TrinkwV sets a technical action value of 100 colony-forming units per 100 millilitres (100 CFU/100 ml) for Legionella spec. It is often searched as the “Legionella limit”, but its legal role is to trigger the operator’s duties when reached. It does not by itself prescribe one universal closure measure or show where contamination originated. The finding must be assessed in the context of the installation, exposure and the people affected.
At or above that value, the approved laboratory has a duty to notify the health authority. The operator must ensure immediate notification if it has no proof that the laboratory has already done so, investigate the causes with a site inspection and a check against recognised technical rules, prepare a written risk assessment and take the required protective measures. The operator reports its measures to the authority and provides the assessment on request. Once the operator has the assessment result and any restrictions or recommendations, affected consumers must be informed without delay under § 52(3). Completed measures must be documented and the records kept available for ten years.

• Maintain one register for system type, operating responsibility, representative sampling points and next due date at each property.
• Store laboratory reports alongside diagrams, access records, risk assessments and evidence of corrective work.
• Assign a person to act on incoming reports immediately and coordinate communication with occupants and the health authority.

Wowworks can help facility teams coordinate suitable local plumbing contractors and track technical work at commercial sites. The operator commissions the approved laboratory and qualified risk assessment, and retains control of notifications and statutory decisions.

Wowworks helps facility teams coordinate suitable local plumbing contractors for technical work at commercial sites in Germany. When a drinking-water investigation identifies a need for corrective work, the team can organise contractor access and track work orders and completion records centrally. This supports follow-up across several properties. The operator remains responsible for commissioning the approved laboratory and qualified risk assessment, notifying the health authority and deciding on the required protective measures.