The decline of global water resources

With the decline of global water resources particularly in South Africa measures have to be introduced to limit water usage. Agriculture is responsible for most of the water consumption in Africa (Madungwe & Sakuringwa, 2007). Greywater is wastewater generated from domestic activities such as dishwashing, laundering and bathing. 50-75% of residential wastewater is grey water ( Eriksson, 2002; Friedler 2004). Countries such as Australia, Lebanon, Mexico, Egypt, and Israel have adopted greywater recycling (Madungwe & Sakuringwa, 2007) . Using untreated greywater in gardens can reduce water consumption by 30% (Jeppesen, 1996).

Studies have been done on the physical, biological and chemical constituents of each type of greywater and its effect on the plant and soil health. Laundry treated greywater contains traces of soap that are rich in nitrates. Nitrates are beneficial as it can act as a pesticide and fertilizer (Finley, 2009). Grey water high in salt and pH may weaken soil structure and fertility (Gross 2005; Qian and Mecham 2005). Grey water with a high pH ( 9.9) can lead to a rise in soil pH which can lead to micronutrient deficiencies ( common under salt stress) and to macronutrient deficiencies (phosphorous), this can lead to decreased growth rates(Jenks and Hasegawa, 2008).

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Some studies results showed that greywater irrigation reduced leaf chlorophyll amounts which could in turn reduce the amount of light collected in plants relative to tap water treatments thus impacting the rate of photosynthesis, (Moradi and Ismail (2007)). However, if the grey water irrigation systems for gardens and crops are designed and maintained with the right care, greywater can be used safely without environmental or health risks (Alfiya 2013).

Treating greywater can be done in numerous ways. This can be done by UV disinfection, sand filtration, or filtering through organic composts like mulches and barks. This however is expensive. (Friedler 2006; Morel and Diener 2006; Li 2009; Dalahmeh 2011; Ghaitidak and Yadav 2013). Filtering in a domestic setting can be done with a nylon stocking for budgeted greywater reuse, this will remove any potential clogging factors such as hair and any solid products found in greywater.

Experiments have been done on carrots and spinach. These crops were irrigated from collected bathing, laundry and dishwashing grey water from numerous households in Cape Town. Spinach plants produced a higher yield when irrigated with grey water but many plants had a leaf-spot disease. Carrots irrigated with grey water did not grow as fast compared to those irrigated with normal water. (Mzini, Loyiso. 2013). Salt and Boron tolerant plants such as a tomato grew normally when watered with grey water (Bino, 2003, Bauder 2007). Plant growth appears to be determined by the type of plant and grey water used (Mzini, Loyiso. 2013). Kidney beans (Phaseolus vulgaris) have not yet been investigated. Phaseolus vulgaris has an optimum growth rate between the pH of 4.2 -6.0 (Duke, 1998). Kidney beans will be used in this experiment as it is a high source of protein that is a common food source.