While grey water re-use is common practice in rural South Africa, urban South Africa are still debating the merits of water quality, public health, considering socio-economic factors, community perceptions and hydro- geologic conditions.
What is Grey Water?
Grey water is made up of water from the bath, shower, bathroom sink and washing. It is not advisable to use your kitchen water as it might be damaging to plant life because of the fat content. Grey water also does not include used water from the toilet as that water is called “black water”. Most of the concerns about grey water have to do with the hygiene aspect and the odours of the water, but both these aspects are eliminated if the water is re-used as soon as possible. Allowing grey water to pool for extended times, can lead to contamination.
Where to re-use?
The average suburban garden accounts for about 35% of domestic water consumption in South Africa. It is therefore useful to know that grey water can be re-used for activities such as gardening, agriculture, aquifer recharge, aquaculture, firefighting, flushing of toilets, industrial cooling, parks and golf course watering, formation of wetlands for wildlife habitats, recreational impoundments and essentially for several other non-potable requirements.
The potential reuses of water depend on the hydraulic and biochemical characteristics of wastewater, which determine the methods and degree of treatment required. While agricultural irrigation reuses in general, require lower quality levels of treatment, domestic reuse options need a higher treatment level. The level of treatment for other reuse options lie between these two extremes.
Re-use for indoors
The easiest applications of grey water include washing floors, windows and cars. Washing carpets, as well as wiping off window sills and security gates are other applications for grey water. Often, consumers judge the capacity to re-use water by the colour quality of the water. This should not be the criteria when deciding to re-use water. Should the colour of the water influence its re-use inside the house, it can always be used in the garden.
Re-use for agriculture
The oldest and largest reuse of water is for the irrigation of agricultural crops. If poorly planned and managed, the potential constraints in this type of application include surface and groundwater pollution, low marketability of crops and low public acceptance of crops. The quality of soil and crops, as well as public health concerns related to pathogens in the water should motivate the proper planning of water re-use for agricultural purposes.
Many research studies have however proved that in addition to providing a low-cost water source, other side benefits of using wastewater for irrigation include increase in crop yields, decreased reliance on chemical fertilizers, and increased protection against frost damage.
Re-use for landscaping
The application of reclaimed wastewater for landscape irrigation includes use in public parks, golf courses, urban green belts, freeway medians, cemeteries, and residential lawns. This type of application is one of the most common applications of wastewater reuse worldwide.
Examples of such uses can be found in USA, Australia, Japan, Mexico and Saudi Arabia among others. These schemes have been operating successfully in many countries for many years without attracting adverse comments.
The soap and other residues in the water can provide useful sulphates and nitrates, when diluted and in some instances it can act as a fertilizer and therefore be beneficial to the garden. This type of application therefore has the potential to improve the amenity of the urban environment.
However, such schemes must be carefully run to avoid problems with community health. Because the water is used in areas that are open to public, there is potential for human contact, so reuse water must be treated to a high level to avoid risk of spreading diseases. Other potential problems of application for landscape irrigation concern aesthetics such as odour, insects, and problems deriving from build-up of nutrients.
By segregating the “grey” silage from “black” toilet wastes, the potential for reuse with minimal treatment within the household enhances manifold. There are several different schemes for reusing grey water at the household levels. In California in the United States, systems which use treated grey water have been in use for many years and studies have shown no health problems associated with the use. In non-sewered areas of Australia, a simple valve arrangement for diversion of bathroom grey water for garden watering has been developed.
Several countries around the world, including Japan, the United States and Australian authorities introduced comprehensive guidelines for grey water recycling systems in individual households. The separation of grey water at the household is being implemented by these countries with great success.
The potential ecological benefits of grey water recycling include deep percolation, lower fresh water extraction from rivers and aquifers, less impact from septic tank and treatment plant infrastructure, as well as topsoil nitrification. A reduction in energy use and chemical pollution from treatment, increased plant growth, the reclamation of nutrients and greater quality of surface and ground water are only some of the potential benefits that necessitates policy intervention around grey water use in South Africa.