Legionella assessments and disinfections

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What is water system disinfection and why is it important?

Water system disinfection is a controlled process designed to remove harmful bacteria, organic matter, and other contaminants from hot and cold water systems. It plays a vital role in maintaining hygiene, preventing Legionella growth, and ensuring systems remain safe and compliant.

At Complii, we deliver comprehensive water disinfection and cleaning services in line with ACoP L8, HSG274, and BS 8558:2011. Our accredited engineers disinfect and certify new installations, refurbished systems, or existing infrastructure following periods of inactivity or contamination. Every service is fully documented, giving you complete confidence that your system meets UK safety and regulatory standards.

Disinfection

UV disinfection

Ultraviolet (UV) disinfection offers a highly effective, chemical-free solution for controlling microorganisms in water systems. By using UV light to deactivate bacteria, viruses, and other pathogens, it provides a safe and sustainable method of maintaining water quality without altering its chemical composition.

At Complii, we design, install, and maintain UV disinfection systems for a wide range of commercial and industrial applications. Each unit is engineered for reliability and precision, helping clients achieve compliance, reduce operational risks, and ensure the ongoing safety of their water supply.

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Why choose Complii?

How we can help.

Protect your people, property, and business. Here’s why we’re the right choice for disinfections.

Maintains system hygiene

Regular cleaning and disinfection remove biofilm, scale, and organic matter that provide nutrients for bacterial growth, keeping your system clean and safe.

Prevents Legionella and microbial contamination

Disinfection minimises the risk of Legionella and other harmful bacteria developing within your water systems, protecting staff, visitors, and building users.

Ensures legal and regulatory compliance

All services are delivered in accordance with ACoP L8, HSG274, and BS 8558:2011, supporting compliance with the Health and Safety at Work etc. Act and COSHH regulations.

Protects new and refurbished installations

Before being brought into use, new or modified water systems must be disinfected to ensure safe commissioning and avoid introducing contaminants into the wider network.

Provides verified documentation

Every disinfection includes certification, test results from UKAS-accredited laboratories, and a full report suitable for audit or submission to utility providers.

Reduces operational risk and downtime

By maintaining clean systems, you prevent costly remedial works, avoid waterborne infection risks, and ensure uninterrupted supply and operation.

Your questions answered.

BS 8558:2011 specifies disinfection following new installations or refurbishments, prolonged system inactivity, contamination events, major maintenance work, or when microbiological sampling indicates bacterial growth.
Yes. For mains water supplies with an internal diameter of 50mm or more, disinfection must be completed and certified before connection, as required under the Water Supply (Water Fittings) Regulations 1999.
The process includes system flushing, chlorination with a controlled hypochlorite solution, a defined contact period, flushing with clean water, and sampling to verify bacterial absence.
Complii provides a full disinfection certificate, method statement, and UKAS-accredited laboratory results confirming chlorine levels and microbiological quality, meeting all water authority standards.
We disinfect all types of hot and cold water services, storage tanks, distribution pipework, mains supplies, and specialist systems such as cooling or process water.
Frequency depends on usage and risk. As a guide, systems should be disinfected during commissioning, following any significant works, or whenever a risk assessment identifies contamination concerns.

Disinfections.

What is water system disinfection and why is it important?

UV disinfection

How we can help.

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Compliance with confidence.