External mains chlorination requirements can vary depending on the water authority. This guide explains the differences between Severn Trent, Thames Water, Anglian Water and others, and why not all chlorination jobs are priced the same.
If you’re installing new external MDPE mains pipework, you’ll usually need chlorination before the system can be connected to the public water supply.
However, one thing that often causes confusion is:
Not all water authorities require the same testing or certification
This means that:
The process can vary
The documentation required can differ
And importantly, the cost is not always the same for every job
In this guide, we’ll break down the key differences between water authorities and explain what you should expect.
WHY REQUIREMENTS DIFFER
Each water authority operates under its own procedures and standards, even though most work is carried out broadly in line with BS 8558.
This means:
Some require pressure testing
Some don’t
Some require specific lab results
Others accept more basic certification
Understanding this early can help avoid delays and unexpected costs.
COMMON REQUIREMENTS BY WATER AUTHORITY
Severn Trent Water
Typically requires:
Pipework chlorination
Pressure testing
Microbiological sampling
This is one of the more complete compliance processes, which can increase time and cost.
Thames Water
Often requires:
Chlorination
Sampling
Pressure testing is not always required for connection approval.
This can make the process slightly quicker and more straightforward compared to other regions.
Anglian Water
Requirements can vary depending on the project, but generally include:
Chlorination
Sampling
Compliance with connection standards
Yorkshire Water
A key difference here is:
They often require NLF (No Legionella Found) results
This means:
Sampling must meet specific reporting criteria
Lab results must be clearly compliant
Southern Water
Southern Water typically requires:
UKAS-accredited quantitative results
This means:
Testing must be carried out through approved laboratories
Results must meet strict reporting standards
WHY SAMPLE RESULTS ARE NOT ALL THE SAME
One of the biggest misunderstandings is assuming that:
“A sample result is just a pass or fail”
In reality:
Different water authorities require different formats
Some accept presence/absence
Others require detailed quantitative results
Some specify how results must be reported
This affects:
Lab choice
Cost
Turnaround time
WHY COSTS DIFFER BETWEEN PROJECTS
Because of these differences, not all chlorination jobs are equal.
Costs can vary depending on:
Whether pressure testing is required
The type of sampling required
Lab testing standards (e.g. UKAS quantitative)
Size and complexity of the system
Number of samples needed
Example:
A job requiring:
Chlorination only
Will cost less than a job requiring:
Chlorination
Pressure testing
UKAS lab sampling
Multiple test points
COMMON ISSUES THAT CAUSE DELAYS
From experience, the most common problems include:
Incorrect sampling requirements
Using the wrong lab
Failing to meet specific authority standards
Missing pressure testing where required
Poor flushing leading to failed samples
These issues can lead to:
Re-testing
Re-chlorination
Delays to connection
HOW TO AVOID PROBLEMS
To keep your project running smoothly:
Confirm requirements with the water authority early
Use experienced contractors familiar with different regions
Ensure correct sampling procedures are followed
Allow time for testing and results
WORKING WITH MULTIPLE WATER AUTHORITIES
If you work across different regions (e.g. England and Wales), it’s important to understand:
There is no “one size fits all” approach
Each project needs to be handled based on:
Location
Authority requirements
System design
Need Help With Mains Chlorination or Connection Approval?
We carry out external pipework chlorination across England and Wales, working in line with the requirements of different water authorities.
We can advise on what’s required for your specific project and help ensure everything is completed correctly to avoid delays.