Dos and don’ts for greywater use at home

In places where water is becoming scarce, people are always looking for new sources of water. One source that is grabbing more and more attention, is the water that we have already used or, greywater. 

However, greywater use comes with a warning tag attached. This is especially true if you live in places where there are no greywater treatment systems (South Africa, I’m looking at you!). So, here, we (the water users) have to ensure that greywater is used right, in order to keep us, our families, pets and whoever else visits our homes, safe. 

Because of this, researchers from the Future Water Research Institute at the University of Cape Town (UCT), and the Division of Community Health at Stellenbosch University, recently wrote the Guidelines for greywater use and management in South Africa. The work was funded by the Water Research Commission, and I wrote an article on it for one of my all-time favourite magazines, the Water Wheel. 

This information really is valuable, especially since we don’t yet have national laws here in South Africa that tell us how greywater use should be tackled. Of course, the guidelines apply to anybody that lives in country where the situation is the same. For that reason, I share the article with you here (edited and shortened a bit):

Guidelines pave the way for safe greywater use

Today, it’s commonly accepted that more people will need more water, while the water available is dwindling. Greywater is being thrown into the mix as a possible water source – an important, and available tool, in the arsenal to increase water security, particularly during times of drought.

Greywater is the water that is left over after you’ve used it in your house for stuff like taking a bath or a shower, washing your hands and doing the dishes and the laundry. It does not include water from from the toilet.

Different lives, different greywater 

In South Africa, your experience with greywater would have been very different, depending on where you live. In serviced areas, where homes have taps and sewage systems, water comes into your house when you open the tap, or flush the toilet. Now relatively dirty, depending on what you used it for, it is washed away again down the drain. In some places that went through drought, like parts of Cape Town, you probably started using your greywater for other purposes recently. Instead of pulling the plug of your bathtub, you might have been scooping up this water in a bucket to use it in other places like flushing your toilet. This often happens during droughts, because there are no other alternatives.

If you are living in an informal settlement, where there are no municipal sewage and water services supplied in your home, you already use greywater extensively, both during drought, or not. You would collect water with a container from a communal tap and use it over and again – first to bath, maybe for more than one person, and then perhaps to do laundry and wash the floor, before throwing it outside.

Still, in South Africa, though we have some municipal guidelines, we do not have national legislation to tell us how to safely use greywater. The Guidelines for greywater use and management in South Africa lays the foundation for this. The document provides a South African context for greywater as an alternative source of water (though not for drinking purposes). The guidelines are based on existing knowledge and expert opinion, and were written to be used as background for national and local government policy-makers to write suitable laws and guidelines.

Greywater quality makes a difference      

Project team leader, Dr Kirsty Carden, senior research officer at Future Water explains that the current drought has sharpened people’s minds to alternative water resources such as greywater. But in South Africa, the management and risk of greywater is different than in many other countries where it is commonly used, because we generally do not make use of greywater treatment systems.

Here, most greywater is collected by hand with a bucket from the shower or bath, or some people might have a small system installed to divert the water from their house to the garden, for example.

“The quality of this water can be very poor, and certainly not without health concerns,” she says. Testing the exact quality of any greywater in a household is not practical, but knowing what you are working with is very important, because it affects what you can use it for. 

Classifying greywater 

Instead, greywater is often classified according to where it comes from, and divided into different classes as follows: 

  • Class 1a: Bathroom greywater – greywater sourced from showers
  • Class 1b: Bathroom greywater – greywater sourced from basins and baths
  • Class 2: Laundry greywater – greywater sourced from laundry basins and washing machines
  • Class 3: Kitchen greywater – greywater sourced from kitchen sinks and dish washing machines.

The guidelines does not include class 3 water (kitchen greywater), because this water can be highly alkaline and contains high concentrations of organic material, fats and oils. Regardless, around 50% to 75% of water used in a household can potentially be reused instead of being washed down the sewer. According to the project report, the amount of drinking-quality water used in South Africa could be reduced by up to 50% should greywater be used for toilet flushing and garden irrigation.

The quality of greywater is very inconsistent, and depends to a large extent on the household in which it is generated – particularly the number of people living in the house, their lifestyles and ages. Households with babies, small children and pets produce greywater that contain higher counts of faeces and urine. Homes where people live with acute diseases such as gastroenteritis, eye / ear infections or jaundice can produce greywater with considerable loads of bacteria. Even if the kitchen sink water is excluded, soaps and detergents, fabric softener, medicines, disinfectant, food particles, pesticides, cosmetics and fibers can make their way into greywater. Saliva, sweat, body oils, hair, blood and some urine and faeces are all part of the potential ingredients of greywater. As such, greywater use  can carry significant risk, both to people and the environment.

The risks of greywater use

These risks include disease, when people come in direct contact with water, or eat food watered with greywater that contain pathogens (bacteria or viruses that cause disease). The high sodium content from soaps, shampoo and body wash can degrade soil, potentially causing long-term problems. Zinc from some hard soaps can also accumulate in the soil, and eventually contaminate groundwater. (Interestingly, studies have not found clear indications that so-called eco-friendly products are more suitable for greywater irrigation systems than more common cleaning products.) In addition, the sewerage system can become blocked because less water, and more solids now flow through it.

Furthermore, children, people with weak immune systems, the malnourished, elderly and pregnant women are all more likely to become ill from eating or drinking or coming in contact with contaminated water. In South Africa, this is a sizable portion of the population.

The study concludes that “not enough is currently known about the long-term effects of greywater use on human health and the environment to make definitive decisions about this practice.” The researchers also conclude that the ranges of contaminants and their potential health impacts under South African conditions needs further research. Even then,  greywater use could always pose some health risk. Therefore, a greywater policy should rather include a decision on the acceptable rate of contamination incidents and/or water-related diseases, before greywater use should be reassessed.

Not enough is known about the long-term effects of greywater use on people and the environment

Guidelines for the use of greywater in South Africa

The report states that greywater is best for activities such as watering the garden (untreated greywater) and flushing the toilet[1] (treated and disinfected greywater). It should be noted that the long-term impacts on the environment of irrigating with greywater have not yet been determined.

As a rule, untreated greywater should never be used where susceptible people can easily come into contact with it. 

Things that greywater should never be used for: 

  • Drinking or cooking
  • Irrigating any food eaten raw or minimally processed (leafy vegetables and root vegetables)
  • Washing of pavements, especially when water drains into the stormwater systems
  • Irrigating gardens during or immediately after rainfall
  • Irrigating areas in gardens where children play, like lawns.

When greywater is used, there are some rules that you should always follow. 

Rules to stick to for greywater use:

  • Avoid human contact with greywater, or soil watered with greywater. Children and pets should be kept away from areas that are watered with greywater.
  • Water that comes into contact with a toilet, urinal or a toilet fixture such as a bidet should never be used as greywater.
  • Water that has been used to wash nappies or other clothing soiled with faeces and/or urine should not be used.
  • Water generated by cleaning in the laundry or bathroom, or when using hair dyes or other chemicals should not be used.
  • Water from the kitchen sink or used in the kitchen to wash dishes or food should not be used.
  • Greywater generated by washing clothes / brushes used for painting or for maintaining machinery and vehicles should not be used.
  • Greywater should not be used if anybody living in the premises is suffering from diarrhea, ear or skin infections.
  • Water used to wash animals, such as domestic pets, should not be used.
  • ‘Low risk’ greywater, such as warm-up water from hot taps, rinse water, bath or shower water is preferable.
  • Untreated greywater should not be stored for longer than 24 hours (otherwise it should be treated).
  • Use signs to indicate greywater reuse, and label all pipes.
  • Ensure that hands are properly washed after contact with any form of greywater and reuse system.

Where greywater use has potential 

The study found that, if managed correctly, greywater can potentially still be a promising water resource in South Africa. Low-density, high income areas where health concerns are less pronounced and more greywater is generated, are ideal.

Here, greywater is best for activities such as flushing the toilet and watering parts of the garden where there is little contact with people. 

However, even flushing the toilet has potential for health risks, because  water droplets may become airborne and land on nearby surfaces. Or, it can spray into the air and be ingested through hand to mouth contact if proper hygiene is not practiced.

Greywater can also be used for small scale irrigation, as long as appropriate barriers to risk are in place. Such systems are however complex, so they are not likely to be implemented in urban areas. 

Greywater use is not for everyone 

Greywater use is not recommended in un-serviced settlements in South Africa. Here, people already use greywater many times over before throwing it away. Even then, it’s thrown away in places with no drainage system, so it mixes with toilet water and other wastewater. As a result, the quality of greywater from informal settlements often resembles black water (sewage). This toxic mix of water can be dangerous to people and the environment.

“There’s no further use of greywater in informal settlements,” says Kirsty. The paradox here is that greywater holds great potential for improving households and living conditions in poor rural settlements, and in urban and peri-urban settlements around the major cities of South Africa. The challenge is to identify conditions and limitations under which this should take place. 

Most realistically then, the most promising place for greywater use in South Africa at this stage seems to be in large buildings such as office blocks, public buildings and hostels. Here, greywater  can be collected and treated under proper supervision.

Towards a future with greywater  

How greywater should and could be used very much depends on the context, says Kirsty. The key message is that peoples’ health and the environment should be protected first.

In informal settlements, our first priority should be providing proper services. People living in serviced areas should be able to use greywater as they see fit, but under certain conditions. In large buildings, properly run systems capable of disinfecting water should be put in place. 

Kirsty says that following the study, she would not promote greywater as a viable, safe alternative source of water in South Africa. However, the report was written before they were in the throes of the drought (Kirsty lives in Cape Town). “In that context we were pretty conservative.” As the drought continued, she says it became clear that people were already using their greywater, regardless of the lack of guidance.

There is a sense that greywater use will happen no matter what, she says. The aim is to provide enough information to management authorities, in order for them to provide the best guidance to residents on how to do this. Still, if we are to seriously start thinking of greywater as part of the resource mix, research on the long-term impacts on people, the environment and policy must continue.

“There are gaps in our knowledge of what could happen, particularly in lower income communities that don’t have access to good services and often use greywater. In general we don’t have a good understanding of the impact of greywater on human health, or the long-term impact on the environment.”

Greywater as water source for stronger cities  

Yet, greywater as an alternative resource is one of the basic principles of resilient cities. Traditionally, water is pumped into a city, used and dirtied, and then pumped away again to be disposed of. “We should think about this differently,” says Kirsty. Instead, the quality of water already within a city should be matched with an appropriate use. In South Africa, it is common to use water of a drinkable quality for everything from drinking to washing clothes and flushing the toilet. But it’s not necessary to use water of the same quality for all of these functions. Yet, drinking water is mostly the only option supplied.

Today, we are more aware than ever that we have to plan for uncertainty. To build cities and systems that are stronger in the face of crises such as drought, the development of guidelines on the safe use of greywater is an important step in the right direction. 


[1] Treated and disinfected greywater can be plumbed into the toilet cistern as part of a reuse ‘system’. If greywater is being collected in buckets during times of water scarcity, it is possible to use untreated water to flush toilets. Water should be poured into the toilet bowl.

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