Britons will pour 15 million cups of roast turkey fat down the kitchen sink on Christmas Day, enough to nearly fill an Olympic swimming pool.
New research from the University of Portsmouth has shed light on what happens to this fat once it enters sewers and transforms into a hard, soapy material.
Scientists estimate removing fat, oil and grease from sewer pipes adds up to £50m a year to our household bills.
Dr John Williams said: “Millions will have stretched their finances to the maximum to pay for Christmas without realising they might be storing up hidden costs for later by pouring cooking fat down the kitchen sink.
“Householders who pour fat down the plughole might as well be pouring money down the drain. Many people do not understand how a modern city runs, which is why sewers are abused. Sewer systems are designed to use water to transport waste, so adding fat, oil and grease to that leads to sewer clogging and system failure.
“The costs of removing fat, oil and grease from the sewers are inevitably passed on to consumers.
“Nobody budgets for this, but we all pay the price.”
Sewer blockages also pose serious health risks through the danger of toilets backing up and sewer overflows.
One of the main reasons fat, oil and grease poured down kitchen sinks causes such huge problems underground is that kitchen sink plugholes are connected to sewers. Once underground the oil transforms into a hard, chalky substance, a bit like soap, which is very hard to remove.
Due to the nature of this transformation it is also extremely difficult for water companies to point the finger at specific homes or businesses, such as takeaway restaurants and fast food outlets, which may regularly pour fat oil and grease down the sink.
Dr Williams said two separate mechanisms might be causing these substances to change and become hard and soapy.
The first one is the transformation over time of fatty acids from unsaturated to saturated forms, which is helped along by sewer micro-organisms.
The second process appears to be linked to the way fat, oil and grease deposits form in hard water areas. Increasing water hardness is associated with increased calcium levels in fats, oil and grease, making the residue harder to remove.
Understanding how the deposits are formed will allow experts to tailor the method they use when removing deposits from pipes, resulting in more efficient cleaning techniques.
This discovery comes hot on the heels of a video released by Southern Water which is designed as a fun way to remind customers not to pour fat down the drain.
The film is based on the song Twelve Days Of Christmas, and includes the message ‘Bag it and bin it’. It can be seen at www.youtube.com/user/SouthernWaterUK
Southern Water’s head of wastewater, Simon Parker, said, “We always notice an increase in fat in the sewers around this time of year as so many people are at home cooking Christmas dinners and more fat than normal ends up down the sink.”