How often must an evaporative cooling system be tested for Legionella?

At least every three months in a laboratory (Section 4(3) 42. BImSchV). If test value 1 is not exceeded in any test for two years, a six-month interval is enough, with one test between 1 June and 31 August (Section 4(4)).

For evaporative cooling systems and wet separators: test value 1 at 100, test value 2 at 1,000 and the action value at 10,000 CFU Legionella spp. per 100 ml (Annex 1 42. BImSchV).

How long is the operating log kept?

Five years, counted from the date of the last entry (Section 12(3) 42. BImSchV).

DE · Expiry & renewal tracking

Never miss a laboratory test for your evaporative cooling system

German operators of evaporative cooling systems and wet scrubbers must have the process water tested for Legionella by an accredited laboratory at least every three months (Section 4(3) of the 42nd BImSchV); after two years below trigger value 1, six months suffice (para. 4). Missed tests are an offence.

The 42nd Federal Immission Control Ordinance (42. BImSchV) applies to evaporative cooling systems, cooling towers and wet separators in which water is trickled or sprayed or can otherwise come into contact with the atmosphere (Section 1(1)). Exempt are, among others, systems that stand in a hall and emit into it, and systems whose process water and trickle surfaces are permanently at 60 degrees Celsius or more (Section 1(2)).

The operator of an evaporative cooling system or wet separator carries out in-house checks of chemical, physical or microbiological parameters at least every two weeks. At least every three months the operator has the process water tested in a laboratory for the general colony count and for Legionella (Section 4(2) and (3)). If test value 1 is not exceeded in any Legionella test for two consecutive years, a six-month interval is enough for that test; one test must then always fall between 1 June and 31 August (Section 4(4)).

Sampling and testing are carried out by an accredited testing laboratory (Section 3(8)). After commissioning or recommissioning, the first test is due within four weeks; for systems that run on no more than 90 consecutive days a year, within two weeks of the annual restart (Section 3(7)). Ordering and results are recorded without delay in the operating log, which is kept for five years (Section 4(5), Section 12(3)).

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At a glance

In-house check	At least every two weeks (Section 4(2) no. 1)
Lab: general colony count	At least every 3 months (Section 4(2) no. 2)
Lab: Legionella	At least every 3 months; every 6 months after two years without exceeding test value 1 (Section 4(3) and (4))
Test values and action value	100 / 1,000 / 10,000 CFU Legionella spp. per 100 ml (Annex 1)
First test	Within 4 weeks of (re)commissioning (Section 3(7))
Operating log	Kept for five years (Section 12(3))

Who is responsible?

The duties lie with the operator: it carries out the in-house checks, instructs an accredited testing laboratory, tells it the time, amount and type of any biocide dosing, and ensures it is informed of the results without delay (Section 3(8), Section 4(5)).

If the deadline passes

Anyone who fails to carry out or commission a test or check under Section 4(2) or (3), or does so incorrectly or late, commits an administrative offence (Section 19 no. 7 of the 42. BImSchV in conjunction with Section 62(1) no. 7 BImSchG).

If a test value is exceeded

If test value 1 or 2 is exceeded, the operator has an additional Legionella test carried out without delay. If it confirms that test value 1 is exceeded, the operator investigates the causes, takes action, carries out in-house checks weekly and has lab tests done monthly; after three consecutive tests below test value 1 the normal intervals apply again (Section 6). If the action value is exceeded, the operator informs the competent authorities without delay and within four weeks as set out in Annex 3 (Sections 9 and 10). Cooling towers have their own values and monthly lab tests, or every two months after two years without exceedance (Section 7, Annex 1).

Tracking it with ExpirySuite

Add an entry for each evaporative cooling system and enter three months after the last sampling as the due date.
Email reminders arrive 60, 30, 14, 7 and 1 day before the date and on the day itself. With a three-month interval, the reminders 30, 14, 7 and 1 day before are the most useful.
The laboratory can upload the test report through a secure link that is valid for 14 days and needs no account.
Assign a responsible person, such as the facilities team; emails arrive in each recipient's language. If a date passes, managers get further reminders 3, 7 and 14 days later.

Frequently asked questions

How often must an evaporative cooling system be tested for Legionella?: At least every three months in a laboratory (Section 4(3) 42. BImSchV). If test value 1 is not exceeded in any test for two years, a six-month interval is enough, with one test between 1 June and 31 August (Section 4(4)).
Who may take the samples?: Sampling and laboratory testing are carried out by an accredited testing laboratory (Section 3(8) 42. BImSchV).
Which values apply?: For evaporative cooling systems and wet separators: test value 1 at 100, test value 2 at 1,000 and the action value at 10,000 CFU Legionella spp. per 100 ml (Annex 1 42. BImSchV).
How long is the operating log kept?: Five years, counted from the date of the last entry (Section 12(3) 42. BImSchV).

Sources

Last checked: Oct 1, 2026 · This page summarises official sources for general information and is not legal advice. Check the linked sources for current rules and fees.

Made for evaporative cooling system lab test, Legionella (42. BImSchV) (Germany)

A ready template for evaporative cooling system lab test, Legionella (42. BImSchV) (Germany) with sensible validity defaults, so you enter less and track more.

Reminders on time

Email alerts at 60, 30, 14, 7 and 1 day before each evaporative cooling system lab test, Legionella (42. BImSchV) (Germany) expires, plus overdue escalation to managers.

Assign an owner

Give each evaporative cooling system lab test, Legionella (42. BImSchV) (Germany) an owner and let employees update their own via a secure link — no login needed.