Read Journal 1770 – Vol 67 No 1 Assessing the water-energy-carbon nexus for water supply in the Mgeni System using a water balance approach

In the 21st century emphasis has been placed on carbon footprint reduction and a net-zero future. As a water-scarce country, South Africa will face significant water deficits in almost all areas of water management by 2025 (Gebrehiwot & Gebrewahid 2016). Efforts are being made by water service authorities to increase potable water production to cope with increasing population and climate change. In the Umgeni-uThukela water supply system, Mgeni accounts for approximately 80% of the total water supply volume. One of the major concerns in water production is the energy usage and its resulting carbon emissions. The Mgeni system uses approximately 195 795 MWh of energy to produce the water demand for the system. Carbon accounting plays a critical role in ensuring that South Africa meets its international climate change commitments. This study utilised the National Generation Grid Emission Factor (NGGEF), as stipulated in South Africa’s 2021 Grid Emission Factors Report (DFFE 2024)

The objectives of this study was therefore to: (a) determine the water balance for the Mgeni system, (b) assess the energy usage projection and determine the carbon emissions generated using a carbon balance approach, and (c) determine the future carbon reduction of water losses. The water supply system was analysed using the IWA Standard Water Balance Method, and water losses were determined from the water balance. Further carbon calculations were conducted using the IWA Standard Carbon Balance (Leakage Emissions Initiative). The analysis indicated that the water supplied to the system (SIV) increases from 396 million m3/annum to 510 million m3/annum, while the water losses equate to approximately 133 million m3/annum to 250 million m3/annum. The carbon emissions from majority coal energy generation were approximately 438 526 tCO2/ year in 2018, and were shown in this study to increase to 2 703 060 tCO2/ year in 2050. With the reduction of water losses, this could decrease by about 18–25%. The carbon emissions
produced by renewable energy generation were approximately 333 781 tCO2/ year in 2018, with an expected increase to 1 191 831 tCO2/ year in 2050.

A global study on water distribution systems determined that implementing pressure management could reduce water losses by 38% which ultimately reduces energy consumption
by 20–40% (Danfoss 2018). Furthermore, implementation of active leak detection could reduce water losses from leakages by 50%, which would result in reduction in energy consumption and carbon emissions (Ong et al 2023). The water industry must play its part and reduce its greenhouse gas footprint. To achieve net-zero carbon emissions from water production activities, water conservation and demand management strategies, such as pressure management and active leak detection, must be introduced to reduce water losses, thereby reducing energy usage and carbon emissions.

Keywords: water management, carbon emissions, water losses, water balance, carbon balance