The Truth About Fatbergs: Causes and Prevention
Fatbergs are one of the few drainage stories that reach the front page. They sound mildly absurd, like something from a children’s book, but they are very real and they cost the UK water industry tens of millions of pounds each year to remove. London has been at the centre of the fatberg story, with several record-breaking specimens discovered beneath the city. This guide explains what a fatberg actually is, how it forms, the famous London examples, and the simple domestic and commercial habits that prevent the next one.
What a fatberg actually is
A fatberg is a congealed mass of fats, oils and grease (collectively known as FOG) bound together with non-flushable solids, predominantly wet wipes, sanitary products and other domestic disposables. FOG enters the sewer warm and liquid. As it travels through cooler pipework it solidifies, gradually building up on pipe walls. The wipes and other solids provide structural reinforcement, and the result, over months or years, is a mass that can be the size of a bus.
The chemistry is straightforward. Saponification, the same reaction used to make soap, occurs when fatty acids meet calcium ions from concrete, mortar or hard water. The product is a hard, soap-like compound that adheres tenaciously to pipe walls. Once that base layer exists, every subsequent FOG discharge bonds to it.
Why the name “fatberg” stuck
The term itself appears to have entered the language around 2013, when Thames Water removed a 15 tonne bus-sized mass from beneath Kingston that took crews three weeks to clear. It is a portmanteau of “fat” and “iceberg”, and it captures the underlying physics neatly: only a small fraction of the mass is visible at any access point, while the bulk extends along the pipe for tens or hundreds of metres. The word now appears in technical literature and trade body briefings as a descriptive term, not an informal one.
Famous London fatbergs
The fatberg entered public consciousness through two notable London incidents. In September 2017, Thames Water removed a fatberg from the Whitechapel sewer that weighed an estimated 130 tonnes and stretched 250 metres, more than two and a half football pitches. A section of it was preserved and exhibited at the Museum of London, where it became one of the more unusual artefacts in the collection.
In April 2018, Thames Water dealt with another major mass in Kingston upon Thames, weighing around 30 tonnes. Smaller but still significant fatbergs have since been recorded in Beckton, Hackney and parts of South London. Beyond the capital, Sidmouth, Liverpool and Birmingham have all reported large masses. The pattern is consistent: dense population, restaurant clusters, and high wet wipe disposal upstream of older sewer sections.
How fatbergs form
The formation cycle is depressingly predictable:
- FOG enters the foul drain from kitchen sinks, dishwashers and commercial preparation areas.
- It cools and adheres to the inside of pipes, particularly at joints, bends and at any rough surface.
- Wet wipes, cotton buds, sanitary items and other non-flushable solids snag on the FOG layer.
- The mass grows, narrowing the bore of the pipe and reducing flow velocity.
- Reduced velocity allows more deposits, accelerating accumulation.
- Eventually flow is restricted to the point where surcharge occurs and the line backs up to the nearest manhole or property.
The same process happens at domestic scale inside a private drain. A single household pouring cooled bacon fat down a sink once a week, combined with flushable wipes that are not in fact flushable, will, over a year or two, build a localised blockage. The household-scale grease blockage is the small cousin of the public fatberg.
Why fatbergs cost millions
Removing a large fatberg is a slow, manual operation. It typically requires high pressure water jetting, breaking up the mass with hand tools and shovels, vacuum tanker extraction, and ongoing CCTV verification. Crews work in confined sewer environments under strict permit-to-work conditions. Thames Water has stated publicly that it spends millions of pounds each year on fat and wipe removal across its network. National figures across the UK water industry are estimated in the tens of millions annually. None of that cost contributes to network upgrade, treatment improvement or service quality. It is pure waste, paid for through customer bills.
Domestic FOG disposal: the simple rules
The single most effective preventive action is correct kitchen waste handling. The rules are unglamorous but they work:
- Pour cooled cooking oil and fat into a sealed container (an old jar, a milk carton) and dispose with general waste.
- Wipe greasy pans with kitchen roll before washing.
- Fit a sink strainer and empty it into the bin, not back down the plughole.
- Never pour fat down the sink, even with hot water, and even with washing-up liquid. Both delay solidification but do not prevent it.
- Treat “flushable” wipe marketing as misleading. Wet wipes, even those labelled flushable, do not break down at the rate of toilet paper and are the leading non-FOG component in fatbergs. Bin them.
- Cotton buds, sanitary items, dental floss and nappies belong in the bin, never the WC.
Across the UK, water companies have run campaigns under titles like “Bin it, don’t block it” for years. The technical message is the same and remains accurate.
What restaurants and commercial kitchens must do
Commercial food premises are responsible for managing FOG at source. The applicable framework includes the Water Industry Act 1991, Section 111, which prohibits discharging substances likely to interfere with the free flow of sewers. In practice, that means:
- Installing and maintaining grease management equipment, either a passive grease trap or an active biological dosing system, sized to the kitchen’s output. Sizing follows BS EN 1825 (grease separators).
- Keeping written maintenance and service records.
- Arranging licensed waste removal for separated FOG by a registered carrier.
- Training kitchen staff in correct disposal practice.
Forecourt and vehicle premises have their own variant: the petrol interceptor, which captures fuel and oil contamination before discharge to the foul or surface water network. The principles are the same: capture at source, maintain to a schedule, dispose responsibly.
Local authorities and water companies have powers to inspect premises and require compliance. The reputational and financial cost of being named as the source of a major fatberg is significant.
Wet wipes and the “flushable” problem
If FOG provides the binder of the modern fatberg, wet wipes provide the reinforcement. UK water companies and Water UK have campaigned for years against the marketing of wipes as “flushable”, because the testing standards used by some manufacturers do not reflect real-world drain conditions. A proper flushability standard, the Water Industry Specification “Fine to Flush”, was introduced in 2019 and is now applied to wipes that genuinely disperse in the sewer environment. Wipes without that mark, even those described as flushable on the packaging, should be treated as bin waste.
The practical implication for a North London household is straightforward. Make a habit of reading the packaging of any wet wipe brought into the home, particularly baby wipes, cleansing wipes and surface wipes. If the “Fine to Flush” mark is absent, the wipes go in the bin regardless of how the front of the packet describes them. The same logic applies in commercial settings, where staff toilets and customer washrooms frequently accumulate non-flushable wipes if no clear signage is in place.
Action plan for North London homeowners
If you are a homeowner in Camden, Islington, Hackney or surrounding boroughs and you want to reduce your contribution to the fatberg problem and protect your own drains:
- Adopt the FOG disposal rules above as a standing kitchen habit.
- If you share a drain with neighbours, agree common practice. One non-compliant household upstream affects everyone.
- If your drains have ever blocked, schedule a preventive hydro jetting service every two to three years to remove early FOG and scale build-up.
- If you operate a home food business, take grease trap obligations seriously even at small scale.
When to call a professional
If a domestic drain is repeatedly slowing or smelling, or if you run a food business and you have never had a grease audit, an inspection is the right next step. See drain jetting in N1 for local jetting services, or contact Greater London Drainage for commercial FOG management surveys.
Final thoughts
Fatbergs are funny only at a distance. Up close, they are slow, expensive, environmentally damaging consequences of small everyday decisions. The encouraging part is that prevention is genuinely simple. A jar on the kitchen counter for cooled fat, a bin next to the toilet for wipes, and a properly maintained grease trap in every commercial kitchen would remove most of the problem from the network within a generation. Until that happens, the engineering response will continue to involve hot work, vacuum tankers and large bills. Better, surely, not to feed the next one.
