Pathways to a water-sensitive campus using a living  lab approach – University of Cape Town as a case  study.

Marekwa, Tariro

Pathways to a water-sensitive campus using a living lab approach – University of Cape Town as a case study.

Thesis / Dissertation

2026

Publisher

University of Cape Town

Department

Department of Civil Engineering

Faculty

Faculty of Engineering and the Built Environment

Abstract

Cape Town is a water scarce city which is highly susceptible to climate induced droughts. In 2015 – 2017 the city experienced a 1-in-590-year drought event which sensitised the city to the adverse impacts of climate on water supply. To increase the resilience of the city to such events it was proposed that there is a need to identify various water supply options to augment municipal water supply. In most cities, universities are one of the largest users of water, applying pressure on the finite resource. This study therefore was an exploration of water reuse opportunities in a living lab located at the University of Cape Town, South Africa. To determine pathways towards a water-sensitive campus, two water reuse systems were analysed: rainwater harvesting and a combined rainwater-greywater system. A behavioural model was developed to quantify the extent to which these systems would reduce the demand for municipal water supply. Two non-potable water demands were considered in this study, toilet flushing and irrigation. In the hydrological year 2022 – 2023, rainwater harvesting produced a water-saving efficiency of 63% for toilet flushing and 7% for an irrigation demand. The distribution of the yield showed that rainwater harvesting is only effective in the period between May and September which represents the rainfall period in Cape Town. This demonstrated that rainwater harvesting alone is inadequate as a strategy towards a net zero water scenario as there would be time periods where municipal supply is needed. For a toilet flushing demand ,73% of the total inflow was lost as overflow highlighting that using rainwater harvesting for a toilet flushing demand alone is inefficient. To reduce the overflow other water uses can be added to the system depending on the water quality. The findings revealed that greywater has the potential to compensate for periods of low rainfall. The Hasso Plattner d-school living lab produces an average of 680 litres of greywater per day. A combined rainwater-greywater system produced a water-saving efficiency of 85% for toilet flushing indicating an increase of 22% by adding greywater. For an irrigation demand however, adding greywater increased the water-saving efficiency by only 2%. A similar trend was shown by the time-based reliability with a 28% increase for toilet flushing and no increase for irrigation. Opportunities for optimisation were investigated by assessing the systems' performance over a range of rainfall patterns with changes in storage capacity and roof area. Increasing the storage capacity would be overall beneficial for both water reuse systems if used for a toilet flushing demand. For instance, using a combined rainwater-greywater system for toilet flushing produced water-savings above 90% for all storages above 35kL. The analysis showed that increasing roof area from effective roof area to total roof area had insignificant impact on system performance. In all rainfall patterns except for a dry year, the effect of increasing roof area was less than 10%. For an irrigation demand, an increase in both storage capacity and roof area did not increase system performance in all rainfall patterns. Overall, the results emphasized that both water reuse systems have a poor capacity to meet irrigation demand. This is because landscape irrigation requires large quantities of water which cannot be met by the water reuse systems. This implied that for optimum system iii performance, irrigation would have to be excluded from the systems and replaced with other smaller water demands in addition to toilet flushing. This insight was also further reinforced by the percentage of overflow produced by the toilet flushing demand. In a dry year, the lowest percentage of overflow was 35% and 40% from a rainwater harvesting and a combined rainwater-greywater system respectively. In an ideal water reuse system, all collected water must be used to meet the demand with no overflow thus this indicated that using the water reuse systems for toilet flushing alone is not optimum in all rainfall patterns and would have to be augmented by other water uses. The concept of living labs was elaborated through a qualitative review of living lab case studies from across the world. Three university living labs from Mexico, Belgium and Brazil respectively were analysed to derive characteristics of living labs. The findings from these case studies were compared with the characteristics of newly established Hasso Plattner d-school living lab to identify missed opportunities and provide recommendations for efficient execution of the living lab approach. The study found that the backbone of living labs is user involvement and co-creation with a clear definition of who the user is. An emergent ‘driver' was recognised in the case studies and this driver strongly influenced the characteristics of each living lab.