Water sample collection for verification monitoring purposes

Water sample collection for verification monitoring and analysis are integral components of implementing a water risk management plan (WRMP).  

The results from verification sampling and analysis can provide an indication as to whether control measures implemented within a facility are effective in controlling Legionella and other microbial risks.

Where to collect water samples

Water samples should be collected from points within your water distribution system that are representative of the overall system performance and control. For this reason selecting each sampling point is an important step in the water sample collection process.

Water sample points should include hot and cold water supply outlets. If mixer taps are installed, water samples from both the hot and cold water supply should be collected.

Water samples should also be collected from a variety of fixtures, for example, shower, sinks, baths, basins.

Collecting a hot or warm water sample from a water distribution system that has a flow and return loop

Take a minimum 3 samples from each loop or facility wing. If a facility has multiple floors on a single loop, take 3 samples per floor. One sample should be taken from an outlet location close to the entry point from the hot or warm water supply. Another sample should be taken from an outlet located approximately mid-point in the flow loop. The final sample should be taken from an outlet location close to the return point to the hot or warm water supply.

Collecting a hot or warm water sample from a water distribution system that has no flow and return loop

Take a minimum of 3 samples from each hot or warm water system. If a facility has multiple floors with single hot or warm water distribution systems, take 3 samples per floor. One sample should be taken from an outlet location close to the entry point from the hot water supply (proximal sample). Another sample should be taken from an approximate mid-point in the system. The final sample should be taken from an outlet location close to the furthest point from the hot water supply (distal sample).

Collecting a cold water sample from a water distribution system

Take a minimum of 3 samples from each system or facility wing. If a facility has multiple floors, take 3 samples per floor. One sample should be taken from an outlet location close to the entry point from the main incoming cold water supply (proximal sample). Another sample should be taken from an approximate mid-point in the system. The final sample should be taken from an outlet location close to the furthest point from the main incoming cold water supply (distal sample).

Frequency of water sample collection

The type, number and frequency of water sampling should be determined and identified in your WRMP.

In high risk areas or if positive Legionella test results are returned then more frequent monitoring is recommended.

Additional verification monitoring should also be undertaken if changes to the water distribution system occur. Examples of these include but are not limited to:

  • following a water distribution system disinfection or decontamination event
  • change of a water disinfection process
  • modifications or repairs to a facility water distribution system or services
  • following water storage tank cleaning
  • following an interruption to supply or advice from a drinking water service provider that there has been a water quality incident in the town supply
  • commissioning or re-commissioning of a facility’s water distribution system.

First flush water samples

A first flush, also known as first catch or first grab water sample can be defined as the first volume of water discharged from an outlet when the outlet is turned on.

The intent of this water sample is for it to be representative of the water quality in the outlet and some of the water in between the thermostatic mixing valve (TMV), if one exists, and the outlet. Although the outlet should only be turned on for a short period, the exact length of time may vary. Knowledge of the diameter of the water pipe leading to the outlet would assist in determining how large the first sample should be, as the intent is to only capture water in or immediately behind the outlet.

The results of this water sample will indicate whether the outlet (such as but not limited to tap fittings, shower hoses, sinks) has any microbial contamination.

Second flush or flushed water samples

This is a water sample collected immediately following the first flush of the outlet.

The intent of this water sample is for it to be representative of the water quality in the water distribution system rather than the outlet i.e. the water in the pipe behind the outlet. The length of time required to keep this outlet turned on will also vary.

The results of this water sample will indicate whether there is microbial contamination within the water distribution system rather than just the outlet.

Steps

Main steps for collecting water samples for microbial analysis:

  • It is recommended that before collecting any water samples for microbial analysis, you contact the NATA-accredited testing laboratory you plan to use to undertake your microbial analyses, as they may require water samples to be collected in a pre-determined manner using specific containers or bottles (which they may, in some cases, provide to you). It is also important to clarify with the laboratory how samples are to be transported to the laboratory.
  • Collection of a water sample will typically involve use of a sterile screw cap bottle that has been pre-treated with sodium thiosulphate (sodium thiosulphate will remove any chlorine residual that may be in the water sample).
  • Label the sample bottle with your name, the time and date, and the location from where the water sample was collected.
  • While collecting the water sample unscrew the cap and place the neck of the bottle below the outlet; do not remove the aerator or any other fitting from the outlet and do not touch the neck of the bottle.
  • Keep the cap in your hand with the open side down to avoid it becoming contaminated.
  • Turn-on the outlet and fill the sample bottle until there is a 20mm air gap at the top of the bottle.
  • Do not to touch the inside of the cap or neck of the bottle. Carefully replace the cap making sure you do not touch either the neck of the bottle or the inside of the screw cap.
  • The volume of water sample to collect will vary depending on the type of water sample, the water analyses to be undertaken and the testing methodology to be used by the laboratory.
  • If a sample will take longer than 6 hours to reach the laboratory then an esky with a cool pack is recommended. The cool pack should not directly touch the sample bottle and some paper can be used to separate it from the sample. The water sample should be delivered to the testing laboratory as soon as possible (ideally within 24 hours).

Disinfection of outlets before water sampling

Disinfection of outlets before collecting a water sample for Legionella bacteria is not a routine practice; although it is routine for E. coli sampling.

An outlet may be disinfected before water sampling only in situations where a case of disease has been detected and as part of the investigation of the cause.

Disinfection involves either heating the water supply to the outlet to above 70 ⁰C and flushing for a minimum of 30 seconds, or disinfecting the water supplied to the outlets. The water sample should then be collected as a second flush sample and will indicate the microbial contamination in the water distribution system, rather than the outlet.

Another method used to disinfect outlets is to heat the first 1–2 cm of the outlet (tap fitting) with an electric heat gun to greater than 70 ⁰C. If aerators or diffusers are attached they must be removed to prevent damage to plastic components. This process will remove any microbial contamination at the point of outlet of the fitting. Before collecting the second flush water sample, allow the tap to cool. Re-install any removed outlet fitting on completion.

Note, this method should only be carried out by a trained professional in consultation with your facility safety representative, and cannot be applied to fittings with temperature sensitive components such as shower heads.

Swabbing outlets before water sampling

Swabbing outlets for a microbial sample is not a routine practice for water distribution systems.

An outlet may need to be swabbed only in situations where a case of disease has been detected and as part of the investigation of the cause in order to isolate and identify a specific strain of bacterium.

Record keeping

All record keeping should be undertaken in accordance with your WRMP.

As noted above, you should record the location, the outlet sampled, the type of water sample collected (first flush or second flush), by whom, date, time and any additional comments (for example, room 15 bathroom, hot water tap).

The testing laboratory should supply a chain of custody form which should be completed accurately so that any test result can be traced back to the exact location from which the water sample was collected.

Caution

  • Stringent control measures must be implemented to prevent the risk of scalding during collection of samples from hot water fittings.
  • Care should be taken to avoid contaminating either the surface of outlets or the water sample bottle during the water sampling collection procedure.
  • Care should also be taken to prevent possible aerosol production during the water sample collection procedure.

Resources

Last updated: 29 June 2017