When does Day Zero
arrive — and under what?
As of 14 September 2026 the combined system sits at 75.2%. Cape Town's most recent reported daily use is around 859 ML. Pick a rainfall scenario, drag the consumption fader, and pin a configuration to compare two futures on the same chart.
The shaded band shows the central 50% of 1,000 simulated rainfall outcomes; the solid line is the median. Day Zero arrives when combined storage crosses 13.5% — the City's 2018 operational trigger. Read the methodology for what data feeds the model and what its limits are.
The system stays above 38% through next summer.
At 850 ML/day, dams draw down through autumn but the winter rains catch up before things get tight.
The City of Cape Town's Bulk Water Branch and the Department of Water and Sanitation publish official forecasts. This page is a visualisation tool that explores trade-offs, not a prediction of what will happen.
The model runs at monthly granularity using 4 year columns of history aggregated with 148 weekly storage readings stitched together from City dashboard archives 2017–2026. Real hydrology runs at daily resolution and accounts for evaporation, transfers and inter-basin flows that are not modelled here.
Day Zero is not deterministic. Even at the same starting point, different winter rainfall outcomes produce different Day Zero dates — that's why the headline shows a range, not a single date. The uncertainty is the message.
All inputs to the model are exposed at /api/scenario.json so anyone can rebuild this independently. Documentation at /predictor/api/.