What would happen if the water supply stopped?

Direct thirst is the obvious clock and the slower one: roughly three days without any water, and most households hold at least some bottled or stored water. The faster failure is sanitation, because flush systems, sewers and hospital hygiene all depend on running water, and outbreaks of diarrhoeal disease follow water and sanitation failures reliably in every documented case. Water treatment plants also stop disinfecting when they lose supply or power, so what remains in the pipes becomes unsafe and pressure loss lets contaminants in, which is why boil notices accompany every major outage. The health burden is not hypothetical: unsafe water and sanitation are associated with hundreds of thousands of deaths a year globally under normal conditions. Restoring a system after a full loss of pressure requires flushing and testing the entire network, which takes days even when the cause is fixed quickly.

How confident this is

This is a reasoned extrapolation rather than an observation. The mechanism is understood, but the scale of the consequences depends on assumptions that could reasonably be argued differently.

Everyday systems

• What would happen if everyone on Earth jumped at the same time? Essentially nothing. All of humanity together is about one ten-trillionth of Earth's mass.
• What would happen if the internet went down? Payments fail first, then logistics — most physical supply chains now depend on network connectivity rather than the other way round.
• What would happen if all the power went out worldwide? Water supply is the first life-critical failure — most tap water is pumped, and pumping stops when the grid does.
• How much space would it take for everyone on Earth to stand in one place? About 2,000 square kilometres — smaller than Luxembourg, and less than twice the area of Los Angeles.
• What would happen if GPS stopped working? Timing, not navigation, is the real dependency — mobile networks, power grids and financial systems all use GPS clocks.
• What would happen if money stopped existing? Trade would collapse to what barter can support, and something money-like would be reinvented within weeks.
• What would happen if all the satellites stopped working? Weather forecasting would lose most of its accuracy beyond a day or two, along with navigation, timing and most long-range communications.
• What would happen if all refrigeration stopped? Food waste would rise enormously and the vaccine cold chain would fail — refrigeration is a public health system, not a convenience.
• What would happen if all digital data was lost? Ownership would be the deepest problem — land registries, bank balances and medical records exist almost entirely as data.