SerpApi.Org
It’s a habit most people don’t think twice about — pouring old or leftover milk down the sink. But according to water companies, this simple act can create big problems for your plumbing and the environment. Experts from Thames Water, one of the UK’s largest water providers, are urging households to stop disposing of milk and other fatty liquids down drains, warning that they can contribute to massive blockages and sewage overflows.
Why milk doesn’t belong in your sink
While it might look harmless, milk contains fats and proteins that can stick to the walls of pipes, leading to buildup and eventual blockages. Over time, this residue can mix with other waste — such as oils, meat juices, and grease — to form solid masses known as “fatbergs.” These dense blockages can cause drains to back up, create foul odors, and even flood homes with sewage in severe cases.
“When milk enters the sewage system, it can also deplete oxygen levels in the water, harming aquatic life,” warns Scottish Water. What many people don’t realize is that milk, despite being biodegradable, acts like a pollutant when it’s dumped in large quantities — especially if it mixes with fats and cleaning chemicals.
Experts say this problem has grown worse as modern kitchens rely heavily on sinks for quick disposal. Thames Water reports over 20,000 drain blockages per year caused by fats, oils, and dairy products — costing an estimated £11 million in cleanup and repairs. And it’s not just milk — drinks like tea, hot chocolate, and cream-based liqueurs can have the same effect, as their fat content builds up over time inside pipes.
So, what should you do with spoiled or leftover milk instead? The good news is there are safe and eco-friendly alternatives. First, pour old milk into a sealable container, such as its original carton, and place it in the bin. You can also add milk to a compost bin or dilute it and use it as fertilizer — milk contains calcium and nutrients that can enrich your garden soil. If the milk is still usable, freeze it for future baking or cooking (just make sure to leave room for expansion in the container).
The same rules apply to other fatty or liquid foods. Cooking oils, gravies, and meat juices should never go down the drain — as they cool, they thicken and harden, creating the perfect base for fatbergs. Instead, let fats solidify before scraping them into the trash or collecting them in a jar to recycle at your local waste center.
Coffee grounds are another common culprit. Even if you flush them with plenty of water, they don’t dissolve or break down, eventually clumping together and clogging your pipes. The best solution is to compost them or dispose of them in a food waste bin — many supermarkets even have dedicated coffee ground recycling bins.
Liquid foods like yogurt, gravy, sauces, and soups can also cause issues. Even diluted with water, their fat content can solidify and stick inside your pipes. To avoid this, scrape leftover food into your bin or compost, and use paper towels to soak up any greasy residue before washing dishes.
Finally, Thames Water’s Tess Fayers, director of wastewater and bioresources, says awareness is key: “Our research shows that everyday habits like rinsing food, oil, and fatty liquids down the sink can unintentionally lead to blocked pipes. These issues are especially common during the festive season when cooking and hosting are in full swing.”
