Cities in drying climates face recurring Day Zero drinking-water shortfalls

Background

A growing list of large cities has approached the point where municipal taps would be shut: reservoirs near empty, rationing imposed, contingency plans for queued water collection. Drivers combine multi-year drought, growing populations, over-allocated sources and aging networks.

Observable evidence

• Cape Town (2017-18): the six-dam system fell toward 20 percent usable storage and the city announced a Day Zero date before halving demand (city water dashboard records).
• Chennai (June 2019): the four main reservoirs hit roughly 0.1 percent of capacity and piped supply was cut from about 830 to 525 MLD.
• Mexico City (2024): the Cutzamala system, about a quarter of the valley's supply, fell to roughly 27 percent in June 2024.
• Bogota (April 2024): the Chingaza reservoirs, near 70 percent of supply, fell to 16.5 percent, triggering a full year of rotating shutoffs.
• Barcelona and Catalonia (2021-24): reservoirs fell below 16 percent during a record 41-month drought and a formal drought emergency was declared in February 2024.

Who is affected

Entire metropolitan populations, with the burden concentrating on low-income households (see sub-issues on tanker markets and on network decay).

Scope boundaries

This issue covers municipal drinking-water shortfall in cities and metros. Village-scale and single-source rural failures are covered by separate issues.

Current state vs desired state

Most cities still manage drought reactively, with opaque communication and rain-dependent recovery. The desired state is a portfolio of demand management, loss reduction, diversified supply and transparent crisis governance that keeps taps running through multi-year droughts.

Impact if unaddressed

Health risks, economic disruption, erosion of trust in local government, and a widening gap between households that can buy private water and those that cannot.