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Building water resilience for Stellenbosch University campus through greywater reuse

JG Afrika | Greywater reuse system at University of StellenboschJG Afrika has designed and is implementing one of the largest greywater reuse systems in the country at Stellenbosch University’s (SUN) main campus in the Western Cape to improve campus water supply resilience and reduce dependency on municipal supply.

“The system design and installation comprises two phases which, once complete, aims to flush more than 1 300 toilets used by about 25 000 university students to meet between 20% and 30% of campus water supply (assuming water demand and conservation measures are in place), as well as to supplement campus irrigation,” Benjamin Biggs, a civil engineer in JG Afrika’s Municipal Infrastructure and Sustainability divisions, says.

Sustainable water-management masterplan

We were appointed by Stellenbosch University to develop a sustainable water-management masterplan prior to the severe 2017-2018 Western Cape drought.

The plan focused on reducing potable demand and increasing campus supply resilience by using all identified water sources optimally, as well as avoiding potable water for irrigation. Water-Sensitive (Urban) Design (WSD) principles were used as a framework to achieve sustainable water-management on campus.

JG Afrika developed a comprehensive SUN water balance by first assessing and modelling eight representative buildings. Water characteristics from each type were extrapolated across campus to other similar buildings and calibrated against utility data.

Interventions focused on the top 40 users, comprising 80% of total water demand. WSD principles were then applied according to JG Afrika’s Water-Management Hierarchy, which focuses on first reducing demand before reusing and finally supplementing existing water supplies.

Notably, campus interventions introduced as part of the first “reduce” stage of the Water-Management Hierarchy decreased potable water demand during the drought by more than 50% (this saving reduced to between 30 and 40% post-drought). Reduction interventions included the installation of efficient fittings, addressing leaks and managing system pressures, in addition to educating staff and students in the efficient use of water.

Building water resilience during drought

The next implementation stage proposed in the Water Masterplan involved water “reuse”. Greywater reuse on campus was identified as a viable alternative supply and JG Afrika was appointed by SUN to design and implement a campus greywater system.

To further build water resilience in the future, we are also investigating the possibility of rainwater and stormwater harvesting used in conjunction with sustainable drainage systems to manage aquifer recharge and thereby enable additional borehole abstraction.

During drought conditions in the Western Cape, JG Afrika’s Cape Town office decided to install a rainwater-harvesting system to provide an alternative source of water should municipal supply cease to be readily available. However, implemented as early as 2011, JG Afrika’s own demand-side management at its office had already recorded a 73% saving in water use. Retrofitted old water fixtures with water-saving items began in 2013 through a series of water saving interventions, including reduced irrigation time and waterless urinals. Further measures, such as hold-flush toilets, low-flow taps and showers, were undertaken in 2016 and 2017.

Educational information on effects of the drought and responsibilities of the consumer was distributed to staff and engagement on the suitability of installed fixtures was facilitated regularly with employees. Water efficient retrofits kept office water use below level 6b water restriction targets and reduced utility bills considerably.

Once demand had been reduced, a rainwater harvesting system, comprising 30 kl of storage, activated carbon filtration and UV-sterilisation and a booster system, was installed for flushing toilets and irrigation. This system enabled “off grid” use for between six and eight months of the year and increased municipal saving to 83% from the baseline year. The combined savings realised by the rainwater harvesting system and efficient fixtures under drought tariffs enable a payback of three to four years for all water optimisation measures. With an alternative supply available, the risk of closing the office should “Day Zero” arrive was also eradicated and business continuity guaranteed.