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What are the different types of domestic wastewater?

When most people think of the water that flows as waste from homes or places where people meet or work, they think of sewage.

But this does not account for the different types of wastewater we generate in the UK in huge amounts every day of the year.

The water we use and then send down sinks and toilets as waste is more complicated than that.

This guide details the different kinds of wastewater and what makes each type different. It also explores some reasons why we should not consider wastewater as waste at all.

In fact, it is a precious resource that is recycled in water treatment plants and can also be reused in its ‘waste’ state.

Doing this is going to become increasingly important as we all contribute to preventing the damaging effect of climate change on our plant.

Wastewater – two main types

In simple terms, wastewater can be described in two broad terms: sewage wastewater and non-sewage wastewater.

What is sewage wastewater?

Sewage is wastewater that contains urine and faeces and is generated by everyday human activity.

This includes sewage from homes, restaurants, schools, businesses, public toilets, and hotels.

Anywhere, in fact, that there is human activity. It is, in effect, unsorted wastewater which, due to the way it is managed, contains human waste.

What is non-sewage wastewater?

Non-sewage wastewater incorporates all types of wastewater that do not contain human waste.

It includes water used for cleaning, for example in laundrettes or domestic washing machines, or for other cleaning tasks, such as washing cars, either at home or at commercial car washes.

Other forms of non-sewage wastewater include surface water run-off that enters the sewer system. This can include run-off from car parks that can contain pollutants, such as fuel, oil and engine exhaust residues and tyre rubber.

The hazards associated with these facilities is acknowledged by the need to install interceptor tanks and filtration systems to capture these pollutants before they can enter the wastewater system.

The point about non-sewage wastewater is that it is not, generally, as hazardous to humans as sewage wastewater.

Therefore, if it can be kept separate from sewage, it is possible to reuse it or treat it and dispose of it at less cost, both financially and in terms of energy consumed.

This thinking is at the heart of new ideas for keeping non-sewage water and sewage water separate in the home and in other premises as part of more sustainable ways to use and treat water.

Wastewater in your home

We generate four main types of wastewater in our homes, and they are all denoted by a colour – black, grey, yellow, and brown.

What is blackwater?

Blackwater, also is the name given to wastewater that comes, in a combined form, from your toilet, kitchen sink and dishwasher and leaves your property down the sewer.

It is, in fact, another name for sewage.

Blackwater contains all the stuff we manage to dispose of down drains – poo, pee, food waste, the fats, oils and grease used in cooking (also known as FOG), as well as cleaning and washing chemicals.

Also, sadly, quite a lot of plastic. That is because many of us have the bad habit of disposing of plastic waste in the form of wet wipes, sanitary products and lots of other items (cotton buds, disposable contact lenses, teeth floss, and condoms) down toilets.

In effect, blackwater is a hotch-potch of all the pollutants we generate in our everyday lives and really should dispose of more responsibly.

In terms of domestic wastewater, blackwater is the most potentially dangerous to us humans, in terms of the bacteria, viruses and parasites it contains.

And it’s very harmful to the wider environment.


What is greywater?

Greywater is blackwater without the urine, faeces or food waste.

Also called sullage, it comes from baths, bathroom sinks and washing machines (the ones used for clothes).

There is growing awareness that greywater can also contain plastics, either in the form of microfibres and particles that come from clothing made with man-made fibres or from products such as make-up, toothpaste and body scrubs.

There is concern that these often microscopic particles are getting into rivers and oceans, causing damage and threatening wildlife.

Grey is a good colour for describing it, because once water has been through a washing machine, it does look grey.

It is not clear water but it is not as contaminated as blackwater.

Greywater contains chemicals and cleaning fluids. But it is more suitable for re-use because it does not contain any nasty pathogens.

This is why there is a move to install systems in homes to allow greywater to be used for flushing toilets.

The Royal Horticultural Society recommends that greywater can be used to water plants, as long as the washing machine components come from rinse cycles only.



What is yellow water?

Yellow water is urine. In fact, it is pure urine.

It does not have any other contaminants found in blackwater and greywater, such as faeces, toilet paper, food particles, FOG, or chemicals.

Some people might say, that is a tall ask. How do you separate urine from those other elements?

In domestic homes, currently, it is not easy. However in public access toilets with urinals it would be much easier.

Even in homes, it is possible to install special toilets that have a built-in separate flow system for collecting urine.

This, again, opens up the possibility of storing, collecting and recycling urine rather than sending it though the sewage treatment system.

So, why should we separate urine from other wastewater streams? It is because urine can be turned into a good fertiliser.

It contains nutrients that are readily taken up by plants.

Urine also contains very low levels of heavy metals (much lower than chemical fertilisers) and pathogens.

Currently, though, urine is sent to sewage treatment plants where expensive processes are needed to remove, and dispose of, these nutrients.

The benefits of using urine as a fertiliser are lost.

What is brown water?

Brown water is faeces. It is the sum total of the solid human waste that enters the wastewater system.

Brown water could also be recycled. Properly processed it can be used as a conditioning agent to revive exhausted soils.

Also, it can be diverted to anaerobic digestion to create methane for generating energy – a process increasingly incorporated into sewage treatment plants.

How much brown water does the average family generate?

The answer is, not very much.

Brown water accounts for a tiny fraction of all wastewater generated in a standard domestic home.



Proportions of domestic wastewater

Just how tiny a fraction can be demonstrated by considering the volumes of different types of wastewater generated in an average family home.

The average family of four gets through around 150,000 litres of water every year.

Of that, about two-thirds is greywater – the water used for showers, baths, washing clothes and cars, and cleaning teeth.

Of the rest, around one third of 1% of the wastewater is urine.

And a tiddly one thirtieth of 1% is faeces.

What does wastewater contain and do?

Wastewater contains a wide range of substances and organisms that can have a harmful effect on humans, wildlife and the environment.

The table below comes from a European Union-funded study into the efficient use of wastewater in Mediterranean environments.

It shows the many different ‘components’ of wastewater, the risks associated with them and the environmental impact of their release into the environment.

One component conspicuous by its absence is plastic. In recent years, awareness of the problem of plastic in water courses and oceans has grown rapidly.

As we have already discussed, the wrongful disposal of plastic-based products down toilets, in particular, is resulting in a build-up of tiny fragments of plastic in streams, rivers and seas.

This is having a harmful effect on the environment and wildlife. It is also a risk to humans, who can ingest plastic taken in by fish and shellfish.

There are growing campaigns against this trend, for example Unblocktober, the world’s first annual engagement campaign urging people to take action to protect sewers and seas.

In November 2021, Surfers Against Sewage called on water companies to do more to prevent uncontrolled discharge of sewage into seas and rivers – a process linked with preventing sewer systems overloading during periods of heavy rain.

The campaign revealed water companies issued 5,517 sewage discharge notifications over a 12-month period, an increase of 87.6%.


Component Key risks Environmental effect
Microorganisms Pathogenic bacteria, virus and worms eggs Risk when bathing and eating shellfish
Biodegradable organic materials Oxygen depletion in rivers and lakes Fish death, odours
Other organic materials Detergents, pesticides, fat, oil and grease, colouring, solvents, phenols, cyanide Toxic effect, aesthetic inconveniences, bioaccumulation in the food chain
Nutrients nitrogen, phosphorus, ammonium Detergents, pesticides, fat, oil and grease, colouring, solvents, phenols, cyanide Eutrophication (over-enriching of nutrients), oxygen depletion, toxic effect
Metals Hg, Pb, Cd, Cr, Cu, Ni Toxic effect, bioaccumulation
Other inorganic materials Acids, for example hydrogen sulphide, bases Corrosion, toxic effect
Thermal effects Hot water Changing living conditions for flora and fauna
Odour and taste Hydrogen sulphide Aesthetic inconveniences, toxic effect
Radioactivity Toxic effect Accumulation

Wastewater components in present in domestic wastewater. Source: Efficient Management of Wastewater, its Treatment and Reuse in Mediterranean Countries

Floodwater and wastewater

There is a close relationship between flooding and wastewater.

Floodwater that rises from streams and rivers contains significant amount of organic matter, as well as chemicals and oils washed from roads and other surfaces.

It will also often contain pesticides and fertilisers from fields.

For this reason, flood water of this type that enters the home must be treated as blackwater. This flood water is often referred to as causing Category 3 damage.

Sewer flooding

For the same reason, flooding associated with sewers is also a very serious event. Sewers can cause flooding in three main ways.

Firstly, if the volume of water exceeds a sewer’s capacity, it can back up in the system into homes and businesses, or flood external areas by escaping through manholes.

Secondly, a blockage in a sewer can cause sewerage to back up in the system and escape into buildings or onto open ground in the same way.

A third cause of sewer flooding is damage to pipes, allowing water to escape, or failure of mechanical systems, such as pumping equipment, that results in a build-up of sewerage in one part of the system.

The wastewater released by sewer flooding must be treated as blackwater. It must be removed carefully and taken away for safe disposal. Again, this is referred to as Category 3 damage.

Pollution caused by failure of wastewater networks and sewage treatment systems is so serious that water companies are required to record events and publish data, see table below.

Sewer flooding - three main ways


Water Company Pollution incidents
South West Water 131
Southern Water 102
Anglian Water 28
Thames Water 27
Wessex Water 25
Yorkshire Water 24
Severn Trent 21
Welsh Water 21
United Utilities 19
Northumbrian Water 14
Total for England and Wales 292

Number of pollution incidents caused by water companies for every 10,000km of sewer in England and Wales in 2020. Source: Environment Agency

Fire wastewater pollution

Another cause of pollution is wastewater created by tackling fires. Firefighters may have to pour millions of gallons of water onto fires, especially at large industrial sites.

This water becomes polluted by chemicals, fire residues and other potentially hazardous substances it comes into contact with.

Therefore, as much care as possible needs to be taken to contain fire water run-off and prevent it from entering sewers or watercourses.

Instead, fire wastewater is taken by tanker lorries to hazardous waste sites for safe disposal.

fire floodwater

Greywater flooding

Greywater floods, caused by water from baths, showers, and washing machines, are less hazardous, if the water can be removed quickly. It is referred to as causing Category 2 damage.

If flood water is left standing for some time, it stagnates and can become contaminated with bacteria, which usually creates a very unpleasant smell. Or there is a risk of other hazardous substances mixing with the water.

Therefore, greywater or clean water that escapes in the home and is left to stand for some time must be treated as blackwater and disposed of with greater care.

Also items affected by this water needs to be cleaned more thoroughly with powerful disinfectants, or discarded.

burst - water pipe - greywater flood

Separating surface water from sewage

The issues discussed above are causing the government to consider taking significant steps to reduce the amount of wastewater that enters the sewer and water treatment system.

One measure being considers is separating surface water run-off from household wastewater on modern estates, those built since the 1960s.

Rainwater from roofs would be diverted away from sewers, so the pipes do not get overloaded during heavy rain.

Instead, it would be diverted directly into water courses, or be allowed to soak away into the ground. However, it is still not clear precisely how such a scheme would work or how the high costs would be paid for.

Cleaning up sewage and wastewater floods

It is clear that wastewater is more complicated than many realise.

Different types of wastewater – black, grey, yellow, and brown – bring with them different risks and challenges, in particular for flood cleaning and waste removal.

This is why it is sensible to always turn to professional wastewater and flood cleaning companies if your property is affected.

SafeGroup provides a highly respected flood clean-up and sewage removal service relied on by businesses and home owners across the UK.

Our expert and trained teams will quickly assess the type of wastewater affecting a property, the risks associated with it, and the swift actions needed to remove the water or sewage, and limit the damage to the building and its contents.

Find out more about wastewater and sewage cleaning from SafeGroup. Call 0800 668 1268.


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