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Hlengiwe Cele 
Dual grey- and drinking-water reticulation systems could save SA’s high quality water

Due to the water shortage that South Africa currently faces, municipalities need to start learning to utilise water of inferior quality for uses such as flushing toilets, in an effort to save drinking water.  Such discussions were held during the first municipal roadshow held by the Water Research Commission (WRC), in partnership with the City of Ekurhuleni, on 20 August 2014 in Germiston. The theme for the roadshow was 'water distribution and distribution systems'.

 Irrigation in South Africa uses approximately 54% of the total freshwater demand, followed by another major user, toilet flushing. Domestic toilet flushing consumes between 50 and 70% of a household’s total drinking water supply. In order to deal with this challenge, the WRC funded a study on dual grey- and drinking-water reticulation systems for high-density urban buildings.

Grey-water from showers, baths, hand basins, laundry tubs and washing machines can provide a solution to our water scarcity challenges. A joint pilot study, conducted by the Universities of the Witwatersrand (Wits), Johannesburg (UJ) and Cape Town (UCT), and funded by the WRC, is proving that the use of grey-water can be an effective way of saving our high-quality water.

A dual grey- and drinking-water reticulation system consists of separate pipes that supply grey-water (only for toilet flushing in this project) and drinking water, respectively, to the end user. This is the first dual grey- and drinking-water reticulation system for high-density urban buildings, and was piloted in the School of Civil and Environmental Engineering (Hillman Block) at Wits. 

The system collects its grey-water from 13 hand-basins and conveys it to a 200-litre tank. Prior to the grey-water tank are two 2-mm sieves that collect any solid materials which find their way from the hand-basins. These sieves are cleaned once a week. Prior to the sieves are two chlorinators that disinfect the grey-water to kill any micro-organisms. “The grey-water tank had to be kept small so that water is used immediately” says Dr Adesola Ilemobade, project leader at the Wits School of Civil and Environmental Engineering. The tank has two submersible pumps for directing water to the toilet when the toilet is flushed, using a switch within the toilet cubicle. Necessary measures were also put in place to avoid backflows.

The first phase of the pilot project was installed to flush one female and one male toilet at the Hillman Block. “If accepted by South African municipalities, the project will be beneficial to many water-scarce communities” said Dr Ilemobade. “At this stage the reuse of black water (sewage) is not considered due to the potentially higher public health risks” he further added.

At the time of installing this system a survey, followed by a massive user awareness campaign at Wits, UJ and UCT, indicated a high level of optimism amongst staff and students about the installation of a dual grey- and drinking-water reticulation system on their campuses.

Dr Adesola maintained that the unit offers several advantages, including the reduction in participating households’/institutions’ drinking water bills, and water conservation. In areas with on-site sanitation systems, grey-water reuse may improve the performance of septic tanks; grey-water reuse also supports a growth in greener water strategies.

Mr Jay Bhagwan, WRC Executive Manager for Water Use and Waste Management, said, “There is an urgent need for national regulations that present a consistent definition for various non-potable resources and recommend an optimal management framework. Additionally, there is also an urgent need for a nationally integrated set of guidelines for non-potable water resource quality for specific reuse, and plumbing codes for dual systems.”

The report detailing the installation of the Greywater reuse for toilet flushing in high-density urban buildings in South Africa: A pilot study is freely available from the WRC Knowledge Hub www.wrc.org.za  WRC Report no. 1821/1/11.

For more information on the project contact  Dr. Adesola A. Ilemobade School of Civil and Environmental Eng. University of the Witwatersrand, +27721282903 (mobile) Email: Adesola.Ilemobade@wits.ac.za


Dr Adesola Ilemobade with Wits engineering students
A   Wits student, OO Olanrewaju working on the WRC project -Dual grey- and drinking water reticulation system
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