When does Day Zero
arrive — and under what?
As of 31 July 2026 the combined system sits at 78.4%. 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.
Storage stays comfortable — 47% at the low.
Inflow outruns withdrawal at this scenario; the system finishes the simulation higher than it started.
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/.