LONDON — UK water companies are warning households across the country that festive cooking and bathroom waste could trigger a costly surge of sewer blockages and fatberg callouts over Christmas and New Year’s, Dec. 21, 2025.
The risk rises when fats, oils and grease — known in the industry as FOG — cool inside pipes, harden on sewer walls and bind with wet wipes and food scraps until they form a concrete-like fatberg that can back up toilets, flood homes and spill sewage into waterways.
Christmas fatberg risk: what water firms are seeing
In London and the Thames Valley, Thames Water said it clears up to 75,000 blockages a year and spends up to £40 million annually to unclog and repair pipes. The utility said FOG causes about 28% of its blockages.
Thames Water’s survey points to everyday culprits: Milk was the most commonly poured substance (61%), followed by meat juices (31%). It also found that 25% of those surveyed believed disposable wipes were safe to flush. Tess Fayers, the company’s director of wastewater and bioresources, warned: “The last thing we want is for the festive season to be ruined by blocked drains.”
In the East of England, Anglian Water said its engineers clear more than 35,000 blockages a year and estimates 80% are avoidable with simple changes — from cooling and binning cooking fat to keeping wipes out of toilets.
In the South East, Southern Water said it has dealt with more than 20,000 “sewer fatberg blockages” in 2025. Matt Collins, who leads its FOG and unflushables team, said: “There’s a one-in-ten chance of a fatberg blocking your pipes this Christmas” if people keep pouring fat down the sink.
Campaigners say the scale is national. Waterwise estimates UK utilities tackle about 300,000 sewer blockages a year at a cost of more than £100 million, with around 70% linked to FOG and so-called unflushable items.
Fatberg warnings aren’t new — and the costs can snowball
Today’s alerts echo a long-running drumbeat. A 2016 report noted that post-Christmas cooking oil and grease can congeal quickly, raising the risk of flooding as kitchens go into overdrive.
And the problem can grow beyond any single sink: in 2017, Thames Water crews battled what one account called a “total monster” fatberg under east London — a headline-grabbing example of how FOG and wipes combine underground.
How to stop a fatberg at home
Bin it, don’t rinse it: Let roasting-tin fat, gravy and cooking oil cool, then scrape it into a container and throw it away.
Wipe before you wash: Remove grease from pans and plates first, then wash — it saves water and keeps FOG out of sewers.
Use a strainer: Catch food scraps before they reach the pipework.
Flush only the “3 Ps”: Pee, poo and toilet paper. Wipes and sanitary products belong in the bin, even when packaging says “flushable.”
Skip the quick fixes: Utilities warn against pouring boiling water or bleach down the drain because it can push the blockage deeper instead of clearing it.
Water firms say the biggest wins are small, repeatable habits — especially during the peak cooking days after Christmas. Keep the ingredients out of the pipes, and a fatberg can’t form.
