Water Tank Cleaning in Dubai — Before and After, With EIAC-Accredited Legionella Results
Most water tank cleaning companies show you clean photos. This case study shows you the science behind the clean — EIAC-accredited laboratory results on two tanks, tested both before and after the job, confirming Legionella absence in compliance with Dubai Municipality's Technical Guidelines for Legionella Control in Water Systems.
Project Overview
Client: Facility management company, Deira, Dubai Scope: Full cleaning and disinfection of two potable water storage tanks — Main Tank and Rooftop Tank Team: 3 certified technicians + 1 driver Service date: 16–17 May 2025 Lab testing: EIAC-accredited Testhub Laboratories LLC (Request No. Q1-250517-23) Contractor: Dotless Cleaning Services — DM-FSD Operator's Permit Sr. No. 00292
What the Tanks Looked Like Before Cleaning
The two tanks at this Deira facility showed heavily contaminated water on opening — dark brown colouration throughout, visible sediment on the tank floor, and surface-level contamination consistent with prolonged accumulation and biofilm formation.
This is not unusual for tanks that have been operating for an extended period without documented professional cleaning. In Dubai's climate — where stored water can reach temperatures of 30°C and above — the rate of bacterial and sediment accumulation accelerates significantly compared to cooler environments. The appearance alone made Legionella testing before cleaning a necessary starting point rather than an optional extra.
Pre-Cleaning Legionella Test Results
Before any cleaning work began, Dotless arranged water samples from both tanks through Testhub Laboratories LLC — an EIAC-accredited testing facility operating under Emirates International Accreditation Centre registration LB-TEST-253.
Samples were collected at the facility in Bur Dubai by accredited laboratory personnel using sterile plastic bottles under British Standard BS 7592 sampling procedure, neutralised with sodium thiosulfate, and transported to the laboratory under temperature control.
Testing was conducted against the specification reference DM-HSD-GU44-LCWS2 — Dubai Municipality Technical Guidelines for Legionella Control in Water Systems, using ISO 11731: 2017 methodology.
The Cleaning Process — What Was Done
Stage 1
Pre-Cleaning Visual Inspection The team conducted a full visual inspection of both tanks before draining — checking the tank room for evidence of rodent or bird access, examining external tank walls for corrosion or leaks, inspecting internal walls for scale deposition, slime deposits, and algae growth, and assessing float valves, inlet and outlet pipework for condition. Findings from this inspection were documented.
Stage 2
Tank Isolation and Safe Entry All water inlet and outlet connections were isolated and locked out with tag-out notices to prevent inadvertent reopening during the cleaning operation. Tank covers were opened and tanks were allowed to vent before entry. Safe working conditions were confirmed before technicians entered the tank.
Stage 3
Full Drainage Both tanks were fully drained using vacuum equipment. Partial drainage does not meet Dubai Municipality's cleaning standard — the entire water volume, including settled sediment at the tank base, must be removed before the physical clean begins.
Stage 4
Scrubbing and High-Pressure Cleaning All interior surfaces — walls, floor, ceiling panels, baffles, and structural components — were scrubbed to remove accumulated sediment, biofilm, and deposits, followed by high-pressure washing to clear residual contamination. DM-approved cleaning chemicals were used where required.
Stage 5
Disinfection Following the physical clean, DM-approved chlorine-based disinfectant solution was applied to all interior surfaces by knapsack sprayer, ensuring complete surface coverage. The disinfectant was maintained in contact with all surfaces for a minimum of ten minutes in accordance with manufacturer specifications and DM-FSD requirements.
Stage 6
Rinse and Re-Check All surfaces were thoroughly rinsed with clean water to remove all disinfectant residue. Drainage was repeated. The lead technician conducted a final internal inspection to confirm the tank was in clean, good working order before the refill stage.
Stage 7
Refill and Chlorine Check Both tanks were refilled with fresh water. Residual chlorine was tested to confirm it was below 1 ppm before the tanks were returned to service — a requirement under DM-FSD cleaning standards.
Stage 8
Post-Cleaning Photography and Documentation The lead technician documented the completed clean with post-cleaning photographs and confirmed all work for the completion certificate.
What the Tanks Looked Like After Cleaning
The contrast between the pre-cleaning and post-cleaning condition of both tanks is visible in the photographs above. All accumulated sediment, biofilm, and surface deposits were fully removed. Tank interiors returned to their original tiled condition, structurally sound and ready for service.
Post-Cleaning Legionella Test Results
Following cleaning, disinfection, and refill, Testhub Laboratories returned to the facility and collected post-cleaning samples from both tanks — same methodology, same accreditation, same DM specification reference.
All four samples — before and after on both tanks — returned Legionella Not Detected results. Confirmatory testing confirmed absence of Legionella species, Legionella pneumophila serotype 1, and Legionella pneumophila serotypes 2–14.
The statement of conformity issued by Testhub Laboratories confirms: results are in compliance with specification limit — DM-HSD-GU44-LCWS2 Technical Guidelines for Legionella Control in Water System.
This is the documentation that matters in a Dubai Municipality inspection. Not a service invoice. Not a contractor's own certificate. An EIAC-accredited laboratory report confirming the water in both tanks meets Dubai Municipality's Legionella specification after a DM-FSD approved cleaning.
Documentation Issued to Client
At project completion, the client received the full documentation package:
Work Completion Certificate from Dotless FZC confirming the scope of work, team details, sequence of operations, and service completion date. Pre-cleaning laboratory reports (x2) from Testhub Laboratories LLC confirming baseline water quality. Post-cleaning laboratory reports (x2) from Testhub Laboratories LLC confirming Legionella-free status in both tanks after cleaning. Before and after photographic evidence embedded in the completion certificate.
This package constitutes a complete compliance record for Dubai Municipality inspections and is issued as standard on every Dotless water tank cleaning job.
Why Legionella Testing Matters for Building Water Tanks in Dubai
Legionella bacteria thrive in warm, stagnant water between 25°C and 45°C — precisely the temperature range that stored water in Dubai's rooftop and underground tanks reaches during summer months. Infection causes Legionnaires' disease, a severe form of pneumonia. Pontiac fever, a milder Legionella infection, produces flu-like symptoms that are frequently misattributed.
The risk in building water systems comes not from the tap but from the storage tank. Water leaving the DEWA distribution system is treated and monitored. Once it enters your building's storage tanks, it is your responsibility. Contamination accumulates in the tank between professional cleaning cycles — sediment, biofilm, and stagnant water pockets all create conditions where Legionella can establish and multiply.
Dubai Municipality's DM-HSD-GU44-LCWS2 Technical Guidelines for Legionella Control set the specification: Legionella concentration in potable water storage must remain below 1000 CFU/L. EIAC-accredited testing is the only method that meets this specification for regulatory purposes. Visual inspection of the tank or water clarity testing at the tap does not satisfy this requirement.
About Dotless Cleaning Services
Dotless Cleaning Services L.L.C holds DM-FSD Operator's Permit Sr. No. 00292 (Form DM-FSD-FO68, Rev:03), issued by Dubai Municipality's Food Safety Department, Registration and Permits Section. This permit authorises Dotless to carry out water tank cleaning in the Emirate of Dubai under DM Food Safety Department requirements.
All water tank cleaning jobs include pre-cleaning visual assessment, full drainage and scrubbing, DM-approved disinfection, post-cleaning inspection, chlorine residual verification, and issuance of a completion certificate. EIAC-accredited laboratory testing is available on every job on request — and recommended as standard for healthcare facilities, schools, hotels, and any facility with heightened water safety obligations.
Frequently Asked Questions
Everything you need to know about our services.
A compliant cleaning service should include post-cleaning water quality testing. Legionella testing against DM-HSD-GU44-LCWS2 specification by an EIAC-accredited laboratory is the standard for facilities with regulatory documentation requirements. Dotless arranges EIAC-accredited Legionella testing through Testhub Laboratories as part of its documented service offering.
Need a waste collection? We dispatch same-day.
If your building's water tanks are due for cleaning or you need EIAC-accredited Legionella testing alongside a DM-FSD approved service, contact the Dotless team to arrange an inspection.
