What happens when water leaves your home?
From washing machines to wastewater treatment
Advertisement feature: Please note that the products mentioned in this article were previously provided to the author as a free gift by Dew Products. The author is under no contractual obligation to post, and all opinions expressed below are entirely my own. We would also like to disclose that the Director of The Ocean Literacy Project, Prof. Leanne Hepburn, is also a board advisor for Dew Products.
written by Alana Wilson (with editorial direction from Leanne Hepburn)
Wipe the counter. Rinse the cloth. Watch the suds spiral down the plughole.
It’s such a small, unremarkable moment in your day that you’ve probably never given a second thought to it. The ‘dirty’ water goes down the drain, the mess is gone, and that’s the end of the story.
Except it’s not…
That squirt of cleaner is just starting its journey; through pipes, wastewater treatment plants, rivers, estuaries, and eventually the ocean. We tend to think of ‘away’ as the full stop on the story, when it’s actually just another part of the same system.
So, what actually happens to the things that end up down the drain?
What’s actually in the bottle?
Long before the product goes down the drain, it starts as a series of decisions; in a lab, on a production line, and in marketing meetings deciding what promises should be on the label.
Most household cleaners are mixtures of ingredients that many of us couldn’t identify, let alone explain the purpose of. The basics generally include surfactants to lift grease and dirt, fragrances, preservatives to keep products stable, dyes, and disinfectant ingredients designed to kill or control microorganisms.
Laundry products are a different beast. They have their own mix of detergents, softeners, builders and other additives. And there’s the extra hurdle of the washing machine.
Every time you do a load, tiny fibres are released from clothes, particularly from synthetic fabrics like polyester and nylon. But we’ll come back to those later, because I think they’re a really good reminder that what goes down the drain isn’t necessarily just what came out of the bottle.
None of these ingredients are automatically sinister. The important point is that they are deliberate design choices.
What ingredients are used? At what concentrations? How readily do they break down? How much product do we need to use? And what happens to the ingredients once we’ve used the product?
Even the language on the bottle makes this difficult to decipher. Buzzwords like ‘eco’ and ‘natural’ sound reassuring, but they don’t necessarily tell us much about what happens to a product once it enters our water system. A ‘green’ label doesn’t automatically mean a product was designed with its entire journey in mind.
The pipe: from sink to sewer
Once the product has left the bottle and hit the water, it enters the sewer system, and at this point the individual choice becomes a collective one.
Across England, particularly in urban areas, household wastewater and rainwater can travel through the same combined sewer. During heavy rainfall these systems can become overwhelmed, triggering storm overflows that discharge excess rainwater and wastewater into rivers and other waterbodies to prevent sewage backing up into homes and streets.
This means that the contents of our sinks, showers, washing machines and toilets all become part of the same much larger flow.
On a normal day, wastewater usually continues towards treatment works. Cleaning products, washing-up liquid, laundry residue, medicines, food waste and everything else we put down our drains all become part of a shared stream.
The treatment plant: what it can (and can’t) do
I doubt many of you have ever actually been to a wastewater treatment plant, but I have, and for a science-obsessed 10-year-old it was one of the coolest school trips!
Wastewater treatment is actually pretty impressive at doing what it was designed to do.
Treatment varies between sites, but broadly speaking, wastewater goes through a series of stages. Primary treatment removes solids through settlement. Secondary treatment uses microorganisms to break down biodegradable organic matter. Some treatment plants also have tertiary or more advanced treatment to remove additional pollutants, nutrients or microorganisms.
The important bit to remember is that wastewater treatment isn’t a magic reset button.
Wastewater contains a huge variety of chemicals and materials, and not all of them behave in the same way during treatment. Some substances are broken down, some remain in the treated water, and some become concentrated in sewage sludge. Reviews of wastewater treatment plants have identified a range of emerging contaminants, including pharmaceuticals, biocides, disinfectants and other biologically active chemicals in wastewater streams.
So let’s talk about the sludge.
Sewage sludge is not just thrown away. In England, for example, there are a few options. It can be treated through processes like anaerobic digestion, which breaks down organic matter to produce biogas that can be captured for energy. However, in 2023, around 94% of the sewage sludge dispatched by England’s nine water companies was used in agriculture.
It’s perhaps a surprisingly circular part of the system, but I think it also shows why the story doesn’t necessarily end when something disappears from the wastewater itself. Because what gets removed from the water has to go somewhere.
Freshwaters: rivers as the carrier
Treated wastewater is released into the environment, often into rivers or coastal waters. During storm overflow events, untreated or partially treated mixtures of wastewater and rainwater can also enter waterbodies.
These are the same rivers we use for drinking water abstraction, recreation and fishing, and they provide habitat for everything from insects to otters.
Sometimes dilution is treated as the answer when we’re talking about residues entering rivers; once something is diluted enough, surely it’s effectively gone?
But let’s remember that dilution ≠ disappearance.
Nutrients like phosphorus can contribute to excessive algal and plant growth, which in turn can reduce oxygen levels in the water and damage freshwater ecosystems. Detergents have historically been a source of phosphorus in sewage, although restrictions on phosphates in domestic laundry and dishwasher detergents have reduced their use in the UK.
Other substances can behave very differently. Some surfactants and chemicals break down in the environment over time, while others may persist for longer or have biological effects at lower concentrations. The environmental fate of chemicals ultimately depends on the substance itself, how much is released, how it interacts with wastewater treatment and where it eventually ends up.
The key point here isn’t that every spray of your kitchen cleaner is about to destroy a river. It’s that millions of ordinary household actions are connected to the same water system.
The ocean: the end of the line
Eventually, water moving through a river catchment reaches an estuary or the coast.
The ocean isn’t this distant, separate place from what happens in the home. It sits downstream of an enormous network of rivers, drains and catchments. Activities on land can ultimately influence coastal and marine environments.
And this is what brings us back to the washing machine…
A simple wash cycle can release thousands of textile fibres, depending on the fabric, garment and washing conditions. Wastewater treatment plants can remove a substantial proportion of these fibres, but some are still discharged in treated effluent, while others are transferred into sewage sludge. Research continues to identify domestic laundry as an important pathway for synthetic microfibres entering aquatic environments.
These fibres are tiny enough to be invisible as they leave the washing machine, but they have been well documented across freshwater and marine environments, including in sediments and marine organisms.
But it’s not all doom and gloom. This is actually a really good example of a problem where intervention is possible at several points.
Laundry bags and external washing-machine filters can capture fibres before they enter the wastewater system, while changes to appliance design can also tackle the issue at source. France has become a leader in tackling this problem: since January 2025, new washing machines sold there have been required to include a microfibre filtration system or another solution designed to capture plastic microfibres.
It’s a fairly small, unglamorous piece of hardware.
But it’s also a great example of what happens when we stop asking consumers to solve a system-level problem entirely through individual behaviour and responsibility, and start changing the products themselves.
A different way to design the chemistry
Now let’s go back to the bottle…
If part of the problem begins with what we’re putting into the water system, one approach is to rethink the product before it even reaches the drain.
One example of this is electrolysed water.
If you vaguely remember this term from GCSE chemistry, you’re not entirely wrong. The process uses an electrical current to electrolyse a solution of water and salt, producing different chemical species with different properties. Depending on the process and formulation, these can include hypochlorous acid, which has antimicrobial properties, and a very dilute alkaline solution containing sodium hydroxide, which can help with cleaning and degreasing.
This is the technology used by Dew Products – a useful case study in product design.
DEW Products are made with more than 99% electrolysed water and are formulated without synthetic fragrances. Different products have different formulations: some use hypochlorous acid, others use very dilute sodium hydroxide, and some cleaning products contain additional ingredients such as surfactants.
From an ocean literacy perspective, what’s interesting here isn’t simply that there is an alternative product out there, but the question behind it: what happens when we consider where a product ends up after use as part of how we design it?
And that thinking goes beyond what’s actually in the bottle. Dew also uses refillable packaging, reducing the need for single-use bottles. It brings us back to those decisions made much earlier in the journey: what goes into the bottle, how much we need to use, how it’s packaged, and ultimately what enters our waste and water systems.
We’re not claiming electrolysed water is a magical solution to all the environmental impacts of cleaning products. Producing it still requires raw materials, energy, manufacturing, packaging and transport, like any product. And the environmental performance of any product ultimately depends on its whole life cycle rather than just one ingredient.
But it does demonstrate an important principle: environmental impact can be influenced much earlier in the chain than the moment we stand at our sinks wondering where the dirty water has actually gone. Sometimes the opportunity starts with how the product was designed in the first place.
It’s bigger than what’s in the bottle
Let’s go back to the beginning.
Wipe the counter. Rinse the cloth. Watch the suds disappear.
It’s easy to think the important bit is the cleaning itself; did the surface get clean? Did the clothes come out fresh? Did the disinfectant do what it promised?
But there’s another question, perhaps more important, worth asking: What happens after we’re finished with it?
This question takes us from the kitchen sink to the sewer, from the treatment plant to the river, and from the river to the ocean.
Perhaps more importantly, it takes us beyond individual consumer choices and towards the decisions made much earlier: how products are formulated, how appliances are designed, how wastewater infrastructure is managed, and what we choose to regulate.
Because sometimes the most important part of cleaning isn’t what we remove.
It’s what we leave behind…