Water chlorination to PD855468 and HSG274 Part 2 (BS 8558:2015)


Mains injection and pipe work chlorination

Internal Water Supply - A mains injection or pipe work chlorination is the process of disinfecting and pre-commissioning a building's internal hot and cold domestic system, including all pipe work and storage tanks. This service ensures systems are safe to supply potable water to outlets such as drinking water or showers.

External / New mains Water Supply - When new water mains supply are installed to a site, there is a mandatory requirement by the local water authority for the pipework to be flushed and disinfected in accordance with their own specification.

All new or modified water systems require to have this performed before they can be connected to the mains supply to prevent contamination of the water supply.

The recognised standard for undertaking both of these services work is PD855468 and HSG274 Part 2 (and BS 8558:2015) alongside any additional requirements of specific water authorities.

When is a pipe work disinfection required?

  • In any new installations as part of a building's commissioning procedure.
  • Where major extensions or alterations have been carried out to the water system.
  • If regular microbiological sampling provides a positive result on an existing system for high counts of harmful pathogens such as Legionella or Pseudomonas.
  • If contamination within the water system is suspected.
  • If the water system has not been in regular use and therefore the pipe work has not been flushed regularly.

Other Systems

Closed systems: heating and chilled water (LTHW and CHW) also have pre-commission cleaning and water treatment requirements.

What is involved?

Method Statement for Chlorination Works

Step 1: Method Statement for Chlorination Works

We provide the client with a detailed method statement of the disinfection process and identify the services to be disinfected.

Mains water flush

Step 2: Mains water flush

Mains water is flushed around the system until the supply is clear, removing installation and manufacturing debris from the pipework.


Step 3: Disinfection

The disinfectant is prepared at the required concentration and pumped into the system at the agreed injection point. This is drawn through all points of the system until the disinfectant is detected at the required concentration at each draw off point.

At this point the system is closed and left for the specified contact period. This is typically one hour when using 50ppm chlorine disinfectant.

For systems with known contamination problems W.E.T recommend analysing the water in advance to determine the optimum disinfection process for the specific infection.

Flush the System

Step 4: Flush the System

Provided the disinfectant level has not significanctly deteriorated the disinfectant is neutralised by pumping through a neutralising solution. This in turn is then flushed out with mains water.

Microbiological Sampling

Step 5: Microbiological Sampling

To confirm the efficacy of the disnfection process water samples are taken from the furthest outlets on the system, these are tested for TVC, E-coli/ coliforms, Pseudomonas and Legionella by a UKAS accredited laboratory.

Certificate of Completion

Step 6: Certificate of Completion

Upon completion the client is issued with a disinfection certificate clearly stating that the works have been carried out to BS8558:2015, appropriate for any water authority, as well as subsequent microbiological sample analysis results from a UKAS accredited laboratory.

Why choose W.E.T as your sub-contractor?

  • Strictly compliant:
    Our disinfection services are designed specifically to meet the standards of PD855468 and HSG274 Part 2 (BS 8558:2015), ACoP L8 and the local water authority specifications.
  • Short lead times:
    Our repeat short lead time business and flexible large contracts allow our account managers to accommodate for even the tightest deadlines.
  • Experience:
    W.E.T are partnered with contractors across the UK, building long term relationships on trust and quality of service for over 20 years. Our knowledge and expertise helps us tailor the service to treat known infections.
  • Health and safety:
    Health and safety is a critical component of any contract. W.E.T is accredited by SAFEContractor, Constructionline and our engineers are CSCS card holders. This is in addition to a wealth of experience working on construction sites.
  • Quality standard:
    All disinfection services are managed under our quality standard ISO 9001:2015 to ensure we maintain a high standard of service when on your site.
  • Accredited by the Legionella Control Association:
    Services are carried out under internal procedures which have been accredited by the Legionella Control Association to ensure year round compliance and quality of service to our clients.
  • National Water Hygiene Card Holder:
    All W.E.T engineers are National Water Hygiene Card holders, which is recognised by all UK water companies and is a pre-requisite for any work on the water distribution network.
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