Water Tank Cleaning

Water storage tanks require regular inspection and cleaning to remain in suitable condition. Over time, sediment, scale, debris and other contaminants can accumulate inside tanks, potentially affecting water quality and the condition of the wider system.

London Chlorination and Water Treatment provides professional tank cleaning services for property managers, commercial premises, councils, builders and homeowners. We assess the tank and surrounding system before carrying out the appropriate cleaning process, taking care to minimise disruption wherever possible.

Whether you need a routine clean, cleaning following an assessment or tank maintenance as part of a larger water treatment project, our team provides straightforward advice and professional workmanship.

For tanks within hot and cold water installations specifically, our dedicated hot and cold water tank cleaning page covers that service in detail.

A cold water storage tank is a lidded cistern that holds mains water inside the building and feeds outlets, and often a hot water cylinder, by gravity. Most sit in a loft, a roof space or a plant room. Where every tap is not fed straight off the incoming main, the building almost certainly has one.

In a house the tank is usually in the loft above the airing cupboard. In a block of flats, an office or a school it is more often in a roof-level plant room, sometimes as a pair of linked tanks so one side can be isolated for maintenance. Two checks settle it: a kitchen cold tap that runs colder than the bathroom taps usually means the kitchen is on the main and the rest is tank-fed, and a pipe stub through the eaves is normally the overflow.

Tank material affects how a tank ages. Plastic cisterns are typical in domestic lofts. Glass reinforced plastic tanks are common at medium sizes. Sectional tanks with bolted panels are built on site for large volumes and tight access. Older galvanised steel cisterns are prone to corrosion and are inspected with that in mind.

Water leaves the mains treated and carrying a disinfectant residual. Once it is stored, three things change. The tank can let stored water drift above 20 degrees Celsius in a warm loft or unventilated plant room, and cold water should be held below that figure. An oversized tank, or one in a lightly occupied building, turns its contents over slowly, so the residual decays and water stands long enough for bacteria to establish. Sediment, rust, scale and anything past a poor lid give bacteria shelter and nutrients within the biofilm on the tank surfaces.

Warm, still, nutrient-rich water allows Legionella bacteria to multiply, and it becomes a concern where that water is turned into a spray at a shower or spray tap. That is why tank condition, temperature and cleaning records appear in almost every Legionnaires’ assessment report. Regular inspection and cleaning form an important part of maintaining the wider water system.

None of this is reliably judged from the tap alone. The tank has to be opened and the base, walls, lid, screens, insulation, ball valve, water level and stored temperature recorded. That inspection decides whether a clean is due and what it should cover.

Cleaning is mechanical and disinfection is chemical. Cleaning physically removes sediment, scale and biofilm by hand. Disinfection then treats the cleaned surfaces and the water with a measured chlorine dose to address the bacteria that remain.

The order matters. Cleaning alone leaves live bacteria behind. Dosing alone leaves the debris that shields them. A tank clean should therefore include disinfection, while disinfection alone is appropriate where there is nothing to remove, such as commissioning a new tank or treating pipework after repair. Where pipework is the main concern, see pipework disinfection. Where the system as a whole needs treatment with certification, see chlorination services and certificates.

The cleaning method is consistent. What changes between properties is the isolation, the notice to occupiers, the working window, and the paperwork that has to satisfy a landlord, managing agent or enforcing officer.

Expected downtime is confirmed at survey, since the drain, refill, contact time and flush cannot be shortened without undermining the work.

Tanks are commonly inspected once a year and cleaned when the inspection shows the tank needs it, rather than to a fixed calendar date. There is no single legal interval that applies to every tank. The Legionnaires’ assessment for the building sets the schedule, based on the system, its condition and how it is used.

Where surfaces are clean, sediment is negligible, the lid and screens are sound and temperatures are in range, a clean can wait. Certain findings move a tank up the schedule whenever it was last done: an unsatisfactory or positive sample, a period of vacancy, work on the tank or connected pipework, a damaged lid, screen or vent, stored water running warmer than the incoming mains, discolouration, taste or odour reported at outlets, or a higher-risk population using the building.

Some tanks cannot be cleaned back to satisfactory condition, and it is more honest to say so at survey. The signs are consistent: heavy corrosion in galvanised steel, cracking or distortion in a plastic or glass reinforced plastic tank, a lid that cannot be sealed, and repeated sample failures after a competent clean. The route in those cases is replacement, and a new tank is chlorinated, flushed and sampled before commissioning through our hot and cold water system replacements service. Most other faults are repairs: a perished lid seal, a missing insect screen, damaged insulation, or a ball valve holding the level too high or too low.