SOP on Microbial Testing of Drain Water (Example)

In short: This is an example SOP for testing the microbial quality of drain water by membrane filtration, to check that cleaning and disinfection are working. It is meant for microbiology and production staff. It is an illustrative template: adapt it, and set your own frequency and limits, under your own quality system.

Drain water testing and drain swabs

This SOP samples the water in the drain. Its companion, SOP for microbial monitoring of drain points, samples the drain surface with swabs. A site may use one or both, depending on its risk assessment.

On the regulatory side, EU GMP Annex 1 (2022), section 4.9, says sinks and drains should be prohibited in grade A and grade B areas. In other cleanrooms, air breaks should separate machines or sinks from drains, and floor drains in lower-grade rooms should have traps or water seals to prevent backflow and be cleaned, disinfected and maintained regularly. Annex 1 gives no sampling method, frequency or numerical limit for drain water, so those parts of this SOP are example in-house criteria.

For related water testing, see SOP for sampling and testing of purified water in microbiology and Guide to inspections of high purity water systems.

1. Objective

To describe the procedure for microbial testing of drain water in the production areas and the microbiology laboratory of [site name].

2. Scope

This SOP applies to the drains in production areas and the microbiology laboratory that are listed in the site drain monitoring plan. Drains are not permitted in grade A and B areas (Annex 1, 4.9), so this SOP concerns drains in other areas.

3. Responsibilities

4. Procedure

4.1 Sampling

1. Check the drains in the production area to monitor the effectiveness of cleaning and disinfecting agents.
2. Using a sterile sampling device, collect 100 ml of drain water from each drain into a sterile glass container.
3. Label the container with the drain ID, date and time and take it to the laboratory promptly.

4.2 Tests to perform

• Total microbial count (bacteria and fungi)
• Absence of pathogens

4.3 Sample preparation

1. Filter the sampled drain water through a 0.45 micron membrane filter.
2. For phenolic disinfectants, diluting the drain water with sterile distilled water before filtration usually reduces the disinfectant effect. Before relying on it, show with a neutralisation check that the chosen dilution allows recovery of test organisms.
3. For other types of disinfectant, a validated neutralisation or additional rinsing step is needed.
4. Wash the filter twice with sterile normal saline, 50 ml each time.
5. Place the filter in 100 ml of sterile normal saline and shake well so that the organisms transfer into the saline.
6. Perform the total microbial count and the pathogen tests on this suspension by the site’s standard method.

4.4 Recording and feedback

Count the colonies, calculate the result and record it in the Drain Water (Microbiological Testing) Record. If results exceed the limits, give feedback to Production so that corrective action can be taken, and raise an investigation under the deviation procedure.

4.5 Frequency (example in-house criterion)

Once a month for every listed drain. Set the frequency from your risk assessment; no regulator prescribes one for drain water.

4.6 Acceptance criteria (example in-house criteria)

A limit “per plate” only has meaning together with the volume plated. The filter is suspended in 100 ml of saline (step 5 above), so state in your SOP how much of that suspension goes on each plate, and keep it the same every time so results can be trended.

Set alert and action levels from your own trend data.

4.7 Records and training

Keep the logbook and reports at least 1 year after the expiry date of the respective product batch (EU GMP Part I Chapter 4 section 4.11, or 5 years after QP certification if longer; 21 CFR 211.180(a)), longer if local law or the marketing authorisation requires. Train staff on this SOP under the site training SOP.

5. Annexures

• Annexure I: Microbial Testing of Drain Water Logbook
• Annexure II: Microbial Testing of Drain Water Report

6. Abbreviations

Frequently asked questions

Why test drain water?

Drains can hold biofilm and water-loving bacteria, and backflow or splashing can spread them to rooms and equipment. Regular testing also shows whether the cleaning and disinfection programme works.

Why filter the sample?

Filtration through a 0.45 micron membrane collects the organisms on the filter and lets disinfectant residues be rinsed away, which would otherwise suppress growth and give falsely low counts.

What limits apply to drain water?

None are set by Annex 1 or the pharmacopoeias. Each site sets its own from risk assessment and trending.

References

1. European Commission, EudraLex Volume 4, Annex 1: Manufacture of Sterile Medicinal Products (Commission guidelines C(2022) 5938, 22 August 2022), section 4.9.
2. European Commission, EudraLex Volume 4, Part I, Chapter 4: Documentation (2011), section 4.11.
3. US FDA, 21 CFR 211.180(a), General requirements.