When business-as-usual no longer is an option: water security is at risk

“Not only is it vital that South Africa continues to invest in the development of its physical water infrastructure systems, but we must also invest in the people who manage these systems and maintain our critical ecological infrastructure such as wetlands, catchments, groundwater aquifers, and river systems,” Aurecon Technical Director James Cullis attests.

South Africa has always been a water-stressed country and has developed a complex and highly integrated bulk water distribution system. Johannesburg is the only global city to be located on a continental divide, while South Africa has one of the highest numbers of large dams per capita globally. Therefore, the country’s water-resource expertise and legislation are respected globally.

“Investing in technical and institutional capacity, improved operations, water-use efficiency, and the development of decision support systems is particularly important as we become increasingly dependent on these more complex and stressed water-supply systems. We also need to balance the trade-off between competing demands for an increasingly scarce resource. Financial constraints and a lack of capacity and accountability for the management of our water resources is a constraint requiring innovative solutions, particularly in Africa,” Cullis elaborates.

There are still significant opportunities for improved water-use efficiency through replacing old pipes, reducing leaks, and by implementing new technologies such as low-flush toilets, improved irrigation systems, and pressure-management devices. Smart technologies, improved monitoring, and operational decision support systems are also critical to reduce wastage.

The future will see a transition to more diverse and alternative water-supply options. In particular, the potential for increased reuse of wastewater for both direct and indirect purposes has many advantages. This is increasingly recognised as an important water-supply option for the future, particularly for landlocked countries or regions, including Gauteng. Demand management will, however, continue to be an important component for managing the variability of water supply.

“It is clear that the private sector will have an increasing role in coming up with long-term water solutions,” Cullis adds. Trends include a general move towards more decentralised water supply and treatment solutions, like what is happening for energy, but the private sector will also be critical in terms of providing the financing as part of Public Private Partnerships (PPPs) for water.

“We have undertaken water resource planning and feasibility studies for alternative water-supply options, including deep groundwater aquifers, desalination, and direct and in-direct potable re-use. We are assisting municipalities in terms of access to financing, development

of their digital transformation strategy, and the development of decision support systems to improve operational efficiencies and reduce losses,” Cullis concludes.

“Aurecon undertakes advisory, planning and engineering design for water infrastructure, as well as hydrology, water-resource planning and feasibility studies across Africa. It provides water engineering services to other sectors, including stormwater and flood modeling support for disaster relief, the built environment and transportation sectors, mine-water balances, treatment and bulk water conveyance for the mining sector,“

Aurecon is currently in the process of rebranding as Zutari, after officially announcing the separation of the African business from the Aurecon Group, effective from 1 January 2020.

 

Urban Water Management

The uninterrupted availability for clean water for many industries and companies is a prerequisite for operations. To what extent are companies in South Africa at risk of interruptions in the supply of water, or the supply of quality water of the required standard? Benjamin Biggs, the civil engineer from JG Afrika, considers alternative supply and onsite treatment.

Cape Town’s Drought of the Century forever changed the City’s urban water management landscape. Declared as disaster area in May 2017, the City of Cape Town faced severe level 6b water restrictions – up to 50 liters per person per day. Residents and businesses alike experienced considerable water tariff increases. The possibility of Day Zero threatened business continuity and precipitated a necessary discussion on water security and the value of water as a resource.

Cape Town’s water comes almost entirely from surface water resources (i.e. rainfall run-off into dams), which is captured and stored in six major reservoirs around the city. Supply dependence on surface water resources can reduce supply resilience to climatic shocks, such as drought.

Considering tariff increases and supply stresses; reducing domestic and commercial water demand; as well as associated water costs has become important for industries, homeowners and businesses. Consumption in toilets, taps, showers and irrigation typically comprise 60-80% of potable use in domestic and commercial areas and targeting these water uses became the focus for demand reduction strategies.

Interestingly, business continuity, rather than savings on utility bills, became a primary motivation for de-centralised alternative supply.

Water Sensitive Design (WSD)

WSD is a widely accepted concept internationally that addresses limitations of conventional urban water management. It integrates all aspects of the water cycle with urban design to provide economic, environmental and social (sustainability) benefits. These principles form a framework through which sustainable water management can be achieved.

Fit-for-purpose

‘Fit-for-purpose’ use is important when selecting a suitable alternative supply for a local site. Not all water supply needs to be a potable (drinking) standard. The application, available quantities and associated risk should determine the level of treatment incorporated. Non-potable use within buildings often necessitates altering plumbing networks – a process that is the easiest to incorporate during the design stage.

Source diversification

Source diversification provides resilience against climatic shocks, such as drought. This requires identifying and matching suitable alternative sources with appropriate application(s).

These principles were applied in the design and operation of a greywater system at Stellenbosch University (SUN). One of the largest of its kind in Africa and a Water Category winner at the 2019 South African Institution of Civil Engineering (SAICE) Western Cape Regional Awards, the system was designed to provide fit-for-purpose water for SUN.

Once both installation phases have been completed, the network will flush over 1 300 toilets used by about 25 000 university students to meet a significant portion of campus water supply and supplement campus irrigation. During term time, up to 75 m³/day of greywater can be treated and reused (Phase 1). This capacity could be increased to between 150 and 200 m³/day after Phase 2. 

Eight representative buildings on campus were assessed and modelled. Water characteristics from each type were then extrapolated across campus to other similar buildings and calibrated against utility data to develop a comprehensive campus water balance. Interventions focused on the top 40 users, comprising 80% of total water demand and the WSD principles were then applied according to the Water-Management Hierarchy. Notably, campus interventions introduced as part of the first “reduce” stage of the Water-Management Hierarchy decreased potable water use during the drought by more than 50%.

Alternative water supplies were then investigated. The Water Masterplan identified treated greywater reuse on campus as a viable alternative supply. JG Afrika was appointed to implement a campus-wide greywater reuse system for toilet flushing and irrigation.

In this system, shower greywater from selected residences is isolated from blackwater and redirected into the collection system via sumps, manholes and grit traps and distributed to a treatment plant.  

The treatment plant on site is able to treat, store and distribute up to 100 m³ of greywater a day at a peak supply of 6 l/s. Treatment steps include primary sedimentation, aeration, solids removal/physical filtration and disinfection/sterilisation by means of hydrogen peroxide dosing. The treated water is stored in tanks at the treatment plant for daily use and in future (Phase 2), excess greywater will be boosted into the existing irrigation network.

Treated greywater is pumped to a header tank with a booster system situated on the roof of a residence to pressurise the non-potable network, which includes a municipal potable supply backup. Plumbed directly into the toilets, this network plans to be expanded to supply and collect from additional campus buildings during the second phase of the project.

CASE STUDY: JG AFRIKA’S RAINWATER SYSTEM

Alternative supply

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.

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.

The Water Management Hierarchy

WSD principles can be implemented through this JG Afrika strategy comprising three stages.

1. After a mandatory baseline assessment is undertaken to develop a site water balance that provides an understanding of water use on site, JG Afrika first focuses on reducing demand.  This can be done by, inter alia, installing efficient fittings; addressing leaks; educating staff/users and encouraging behavioural change; as well as managing system pressures. Importantly, reducing demand is emphasised before implementing alternative supply solutions.

This step is critical in decreasing quantities of alternative supply required and, in so doing, reducing installation, operation and maintenance costs, as well as utility bills, while also facilitating good stewarding of precious water resources. Many projects have saved over 50% in water use after implementing these measures.

1. The second stage entails reusing greywater and rainwater in “fit-for-purpose” applications, such as toilet flushing and irrigation
2. Alternative supply from more conventional sources, such as borehole abstraction in conjunction with sustainable drainage systems managed aquafer recharge, river abstraction and treated wastewater reuse, are assessed in the final stage as a last resort.

CONCLUSIONS: CASE STUDIES

WSUD principles, applied to the Stellenbosch University Campus using ‘The Water Management Hierarchy,’ improved the campus water sustainability. The SUN greywater was designed to improve campus supply resilience and provide ‘fit-for-purpose’ water.

JG Afrika demonstrated that demand reduction measures – regardless of implementation scale – can be simple, cost-effective and result in better than expected savings. Installation of efficient fixtures typically do not require behaviour change and only minor maintenance. These measures can be implemented by a local plumbing team and do not usually depend upon additional technical assistance.

Furthermore, rainwater harvesting when used alongside efficient fittings can be highly effective in maintaining business continuity during a drought and reducing utility bills.  

Implementing similar measures to these two case studies on a larger scale could considerably alleviate pressures on regional and national water supply and enable water savings in other offices, homes and campuses.

Biggs is a civil engineer in JG Afrika’s Municipal Infrastructure and Sustainability divisions

“Interestingly, business continuity, rather than savings on utility bills, became a primary motivation for de-centralized alternative supply.”