Quick answer: Water stored in dust suppression bowsers and trailer tanks on construction, quarry and demolition sites presents a Legionella risk if temperature, stagnation and tank hygiene are not actively managed. HSE Approved Code of Practice L8 applies to any water system — including mobile dust suppression tanks — where water is stored and there is a reasonably foreseeable risk of Legionella exposure. The primary controls are temperature management (stored cold water below 20°C), avoiding stagnation, and regular tank inspection and disinfection every six months. Tank colour and material are secondary measures, not substitutes for the primary controls.
Dust suppression on construction sites, quarries, demolition sites and mining operations relies on stored water — in bowser tanks, trailer-mounted units and static site water tanks — to suppress airborne dust at source. The focus is usually on dust control compliance under COSHH 2002 and HSE EH40. What is less commonly considered is the Legionella risk in the water tanks supplying those suppression systems.
Legionella pneumophila thrives in stored water at temperatures between 20°C and 45°C, in stagnant or slow-moving water, and where organic material — algae, biofilm, rust, sludge — provides nutrients for bacterial growth. A dust suppression bowser sitting on a warm construction site in summer, partially used, not cleaned for weeks, can provide exactly those conditions. This is not a theoretical risk — it is a manageable one, but it requires the same structured approach as any other water system under HSE Approved Code of Practice L8.
Does a black opaque tank reduce Legionella risk?
Black opaque tanks are commonly specified for dust suppression and water storage on site. There are genuine benefits — but they are secondary controls, not primary ones.
Sunlight and algae prevention
Legionella needs nutrients to grow. Sunlight penetrating a translucent or clear tank encourages algae growth, which provides a food source for Legionella and other bacteria. A black opaque tank eliminates this pathway by blocking sunlight entirely, preventing algae proliferation. This is a meaningful risk reduction measure — but it does not address temperature, stagnation or biofilm formation on its own.
UV stabilisation
A black tank in outdoor use must be manufactured from UV-stabilised material. Without UV stabilisation, prolonged sunlight exposure degrades the tank material — causing surface cracking, corrosion and structural damage that allows bacterial contamination to enter. Specify UV-stabilised polyethylene or equivalent when procuring site water tanks for dust suppression use.
The temperature risk with black tanks
Black tanks in direct sunlight absorb heat. A black tank exposed to direct summer sunlight can raise stored water temperature into the 20–45°C range — the optimal growth band for Legionella — faster than a white or translucent tank. A black tank is not automatically safer on temperature grounds. It must be properly insulated and positioned out of direct sunlight, or in shade, to maintain stored water below 20°C.
Tank colour and material are helpful secondary measures. They do not replace the primary controls required under L8.
Primary Legionella controls for dust suppression tanks
1. Temperature management
The single most important control. Legionella does not multiply significantly below 20°C and is killed rapidly above 60°C. For cold water stored in dust suppression tanks:
- Stored cold water must be kept and distributed below 20°C
- Hot water systems (where applicable) must be stored at or above 60°C
- Tank positioning — shade, insulation, reflective covers — should maintain stored water below 20°C throughout the working day
- Temperature should be monitored and recorded as part of the site water risk assessment
2. Avoid stagnation
Stagnant water is high-risk water. Legionella multiplies in slow-moving or static water where temperatures are favourable. For dust suppression tanks:
- Size tanks appropriately — a tank that is rarely fully used creates chronic low-level stagnation
- Avoid dead legs — unused pipework or hose runs where water sits static
- Where a bowser or tank is not used for an extended period, drain and clean before returning to service
- Flush the system before first use each day on long-duration projects
3. Regular cleaning and disinfection
HSE guidance requires that water storage tanks are inspected, cleaned and disinfected at least every six months — more frequently where risk assessment identifies higher risk conditions. For site dust suppression tanks, cleaning should include:
- Inspection of tank interior for rust, scale, sludge and biofilm
- Physical cleaning to remove accumulated debris
- Disinfection with an approved biocide at the correct concentration and contact time
- Flushing and refill with fresh water before returning to service
- A written record of all cleaning and disinfection activity
COSHH assessment required for all biocidal disinfectants used in tank cleaning. Note: GB CLP chemical reclassification comes into force August 2026 — all biocide product COSHH assessments must be updated. See: Chemical reclassification August 2026
4. Tank lid and insect screen
A tight-fitting, secure lid with an insect mesh screen prevents organic debris — leaves, insects, bird contamination — from entering the tank. Organic material entering the tank provides nutrients for Legionella growth. This is a straightforward and inexpensive control that is frequently overlooked on site water tanks.
Legionella risk assessment for dust suppression systems
HSE Approved Code of Practice L8 requires that any person responsible for a water system — including mobile and static dust suppression tanks on construction and quarry sites — carries out a Legionella risk assessment. The risk assessment should identify:
- All water storage vessels and distribution points in the dust suppression system
- Temperature conditions across the system during normal site operation
- Stagnation risks — tank sizing, dead legs, periods of non-use
- Tank material, construction, lid and screen condition
- Cleaning and disinfection history and frequency
- Who is responsible for ongoing monitoring and maintenance
On a CDM-notifiable project, the Construction Phase Plan should reference water system Legionella risk management as a site health hazard. The principal contractor has overall responsibility for ensuring the risk assessment is in place and controls are implemented. Further reading: CDM 2015
Anti-microbial tank specification
Anti-microbial plastic tanks — manufactured with silver ion or other biocidal additives integrated into the tank material — can provide an additional layer of protection by limiting biofilm formation on internal tank surfaces. This is a useful specification upgrade for high-risk environments or long-duration projects where cleaning frequency may be difficult to maintain. Anti-microbial tank specification does not replace the primary controls of temperature management, stagnation avoidance and regular cleaning — it supplements them.
V-TUF dust suppression equipment and tank specification
V-TUF's bowser-mounted and trailer pressure washer range is used for dust suppression on construction, quarry, demolition and mining sites. When specifying dust suppression equipment with onboard water storage, the tank specification should be reviewed against the Legionella risk controls above — black opaque UV-stabilised tanks, appropriate sizing for the site water demand, and a lid and insect screen as standard.
For guidance on dust suppression equipment specification for your specific site application, contact the V-TUF technical team: 01522 787978 | enquiries@v-tuf.com
Related guidance
COSHH Regulations 2002 HSE EH40 — Workplace Exposure Limits CDM 2015 Construction hub Oil, gas and mining Chemical reclassification August 2026 Pressure washers Hot water pressure washers
