S7 Ep45: Cape Town's day zero: How data rebuilt a city's water resilience

By 2018 the reservoirs supplying Cape Town were down to 20% of capacity. If they reached 13.5%, the city would need to shut down parts of the water network and send residents to collection points to fetch water. That was known as Day Zero, and the rain came just in time to avoid it.Hugh Cole (City of Cape Town) joined the city government in the middle of the crisis, and has subsequently driven the use of data for many aspects of city planning, not just for water. Cape Town now runs its own household survey, works with a private sector partner to measure net migration, and randomises the rollout of water meters so it can find out how they change behaviour. It also runs trials on its electricity subsidy to check whether the money reaches the households it is meant to reach. Cole tells Tim Phillips how the Day Zero near miss changed how the city's leadership uses evidence, and how other cities can follow the same path.The research behind this episode:Abajian, Alexander C., Cassandra Cole, Kelsey Jack, Kyle C. Meng, and Martine Visser. 2025. "Dodging Day Zero: Drought, Adaptation, and Inequality in Cape Town." NBER Working Paper 33468.Cole, Hugh, Kelsey Jack, Derek Strong, and Brendan Maughan-Brown. 2020. "City of Cape Town, South Africa: Aligning Internal Data Capabilities with External Research Partnerships." In Handbook on Using Administrative Data for Research and Evidence-based Policy, edited by Shawn Cole, Iqbal Dhaliwal, Anja Sautmann, and Lars Vilhuber. Cambridge, MA: Abdul Latif Jameel Poverty Action Lab.To cite this episode:Phillips, Tim, and Hugh Cole. 2026. "Cape Town's day zero: How data rebuilt a city's water resilience." VoxDev Talks (podcast).About the guestHugh Cole is Director of Policy and Strategy and Chief Data Officer at the City of Cape Town, where his department covers strategic policy, strategic planning, research and economic analysis. He is a Visiting Senior Fellow at the School of Public Policy at the London School of Economics. Before joining the city in 2017 he was Director of Country Programmes at the International Growth Centre, running teams in 14 countries across sub-Saharan Africa and South Asia.Research cited in this episodeDay Zero. The term began in the media as the day Cape Town's taps would run dry, then settled on something more specific. It became the day dam levels would hit 13.5%, at which point the city planned to shut down parts of the reticulation network and open water collection points, sequenced so that the most vulnerable communities were affected last.Dodging Day Zero. Abajian, Cole, Jack, Meng and Visser use municipal billing records to show what the emergency measures did to different households. Before the drought, richer households used twice as much piped water as poorer ones; at the peak of the crisis they used less, partly because they could drill boreholes and substitute private groundwater for the public supply. That eroded the utility's revenue and shifted the cost of supply towards households who could not afford a private alternative, which is why the tariff reform that followed matters as much as the conservation campaign did.Zonal water balance assessment. Pressure management in the network was one of the two measures Cole credits with the largest effect during the drought, alongside communication with residents. Managing pressure means knowing the boundaries of each pressure zone, and those boundaries had drifted over years of pipes being added and not always recorded. The remapping exercise that followed compares water entering a zone with water leaving it, and it is still going on.The Green Dot map. During the drought the city published a neighbourhood level map of household water consumption, developed with academic partners including Martine Visser at the University of Cape Town. Households within their usage band showed as a green dot. The aim was peer pressure at street level rather than a citywide number.The Water, Air and Energy Lab. Launched in March 2024 by J-PAL Africa at the University of Cape Town, the City of Cape Town and Community Jameel, the WAE Lab pairs city policymakers with researchers to run randomised evaluations on clean air, water and reliable energy. Kelsey Jack is its scientific advisor. It is part of a network of J-PAL air and water labs that also includes national and state level labs in Egypt and India.Free basic electricity. Cape Town subsidises electricity for low-income households, targeted using thresholds on property value and consumption. Because eligibility