Wastewater Reuse at Home

Domestic water consumption makes up 8% of total global water use (UNWATER 2012). Particularly in developed countries, domestic water use is often many times larger than the WHO minimum recommended per capita consumption. Thus, household water consumption has a large potential to be reduced. Benefits of reducing domestic water consumption include lower water bills or less time spent collecting water, reduced pressure on local water resources, and increased availability of potable water available for appropriate purposes such as drinking, cooking, and hygiene.

One effective way of reducing water consumption is to reuse the wastewater produced at the household level. The reuse of wastewater presents an opportunity to not only save water and financial resources by reducing water consumption, but to simultaneously increase food production or create livelihood. In developing countries, optimising wastewater reuse can therefore be a significant window for development.

A critical aspect for wastewater reuse is that the quality of wastewater must be appropriate for its reuse. There are several different types of wastewater produced at the household level that have very different levels of contaminants (i.e. nutrients, pathogens) and reuse potential, including rainwater, greywater (all household wastewater except toilet flushing water), urine, blackwater, and faeces. Separating these streams of wastewater reduces the amount of wastewater contaminated by pathogens (i.e. blackwater, faeces, urine) by preventing it from coming into contact with less contaminated water (i.e. greywater, rainwater), thereby allowing greywater and rainwater to be used for a wider range of purposes.

By separating these waste streams at the source, it is possible to retain high volumes of relatively safe water (i.e. greywater, rainwater) that can be directly reused, whilst reducing the volume of wastewater (i.e. blackwater) that must be treated before reuse. Particularly in developing countries where water and wastewater systems are non-existent or incomplete, implementing source separation is key in developing sustainable systems that will benefit users over the long term.Depending on the contaminants present in wastewater and its future reuse, wastewater can either be directly reused, or treated and reused (recycled). Similarly, organic waste (such as kitchen waste or toilet waste) can also be reused at the household level to reduce the quantity of waste produced and to gain the benefits of nutrients or energy.

How Does it Work?

Direct Reuse

Water that is of a relatively high quality with few contaminants, such as rainwater or greywater, can be directly reused. Numerous technologies exist for household precipitation harvesting, while greywater can be collected by refitting pipes to divert wastewater from appliances like showers, washing machines, and sinks.

• Even though water for direct reuse may be relatively free of contaminants, the future reuse of rainwater and greywater must be appropriate for the level of contaminants present. Appropriate purposes for direct reuse can include:
• Washing (cars, etc.)
• Flushing toilets
• Gardening and food production can be done with greywater towers, vertical gardens, fertigation, drip-irrigation, and subsurface drip irrigation

Treat and Reuse Wastewater (Recycling)

If wastewater is not suitable for direct reuse, household wastewater treatment options may be employed to reduce the level of contaminants to a level that is safe for reuse. Some possibilities for household wastewater treatment systems include:

• Constructed wetlands (see free-surface, horizontal, vertical, and hybrid constructed wetlands)
• Biogas settlers
• Anaerobic baffled reactors
• Septic tanks
• Leach fields
• Evapo-transpiration beds
• Surface or subsurface groundwater recharge

Once treated sufficiently, wastewater can be used similar as rainwater or greywater, for purposes such as gardening and urban farming, toilet flushing, etc. (see “Direct reuse” above).

Treat and Reuse Organic Waste (Recycling)

Organic waste, such as kitchen waste and toilet waste, can be reused for energy production (biogas) or for compost or soil amendments.

There are numerous technologies that use anaerobic digestion processes to produce biogas, including small scale anerobic digestion, biogas settlers, and anaerobic baffled reactors. Biogas may either be used directly (see direct use of biogas) or to produce electricity (see biogas electricity).

Organic waste can also be reused as fertiliser for growing plants. However, because faeces and excreta contain pathogens that can transmit diseases, treatment must take place before reuse. Composting renders both kitchen waste and toilet waste safe for application to soil, and can be produced in numerous ways. invalid link may be used for kitchen waste as well as faeces and excreta. There are also toilet systems designed to produce on-site useable compost from faeces and excreta, such as composting toilets, fossa alterna, arborloos, or UDDTs and subsequent storage and drying of faeces. An alternative to the conventional composting process is terra preta sanitation which produces high quality compost without odour or gas production (also see terra preta toilets).

Urine may also be used as fertiliser without a composting step if they are properly handled. For this, urine must be diverted from faeces (see UDDT and urine diverting flush toilets) and stored (see urine storage) before being applied to soil (see small scale urine fertilisation).

It is essential that the quality of waste (wastewater or organic waste) is adequate for its reuse purpose. Source separation of wastewater is a way to maximise the potential for wastewater reuse, as different types of wastewater (i.e. rainwater, greywater, urine, blackwater, and faeces) have differing contamination levels of pathogens and contaminants but also nutrients and salts, and are therefore appropriate for different purposes. By separating these waste streams at the source, it is possible to retain high volumes of relatively safe water (i.e. greywater, rainwater) that can be directly reused, whilst reducing the volume of wastewater (i.e. blackwater) that must be treated before reuse.

If the quality of wastewater is not high enough for direct reuse, it must be treated beforehand, or not reused at all. To ensure that the quality of wastewater or greywater is appropriate for reuse, the water quality should be tested for nutrient concentrations, pathogens, and other contaminants.

While the reuse of greywater and wastewater may be encouraged in areas experiencing water scarcity, there are often strict regulations determining the levels of contaminants allowable for reuse, and laws governing what are permissible uses for wastewater and greywater. Many countries (such as the U.S., Switzerland, and Australia) have regulations for wastewater disposal that make reuse prohibitively complicated. Regulations regarding the use of wastewater, greywater and excreta can be found in WHO guidelines for policy and regulatory aspects of safe wastewater reuse.

• Disease-carrying mosquito populations may increase if home treatment involves stagnant water (such as in free-surface, horizontal, vertical, and hybrid constructed wetlands).
• Crossing plumbing lines when refitting pipes can lead to contaminated drinking water, and may be illegal.
• Diseases can be transmitted when using greywater or treated wastewater to produce fruits or vegetables that are eaten raw. To avoid contamination risk when reusing greywater or treated wastewater for food production, refer to WHO guidelines on reuse of wastewater in agriculture and WHO guidelines of reuse of excreta and greywater in agriculture.
• Quality of water might be too risky for reuse if toxic cleansers or sick people are present. For example, many pharmaceuticals (antibiotics, hormones, etc.) are not degraded by wastewater treatment and may therefore be present in high concentrations in urine. Separation of urine from other wastewater streams can reduce exposure to these pharmaceuticals.

• Wastewater (including greywater, blackwater, urine, etc.) is free: reusing it means paying less for potable water.
• Refitting systems to collect greywater can range from zero to hundreds of dollars, depending on the modifications that are necessary.
• Using urine, faeces, and organic waste for plant fertilisation reduces the cost of purchased fertiliser and increases plant productivity.

One example of a household system that has incorporated many technologies for reuse of wastewater is the Eco-Home in Kathmandu, Nepal. See: The Eco-Home. By employing a number of water and nutrient recycling systems, the home has managed to establish nearly closed-loop water and nutrient cycles. The home is not connected to water distribution or wastewater collection systems, and supplies all its needed water with rainwater harvesting that is purified with a biosand filter and disinfected with SODIS. Wastewater and greywater are treated with a vertical flow constructed wetland, and reused for rooftop gardening. Nutrients from urine and faeces are recovered with a composting toilet (SHRESTHA 2010).