Stored water and point-of-use treatment

It works if the supply is cut off or becomes doubtful. The meta-analysis by the WHO and collaborators published in The Lancet in 2022, covering 124 studies, measures reductions in diarrhoea risk compared with untreated water from an unimproved source: point-of-use filtration with a relative risk of 0.50, solar treatment 0.63 and chlorination 0.66. Handwashing with soap reduces the risk by 30% ^[1115]Effectiveness of interventions to improve drinking water, sanitation, and handwashing with soap on risk of diarrhoeal disease in children in low-income and middle-income settings: a systematic review and meta-analysisWolf, Jennyfer; Hubbard, Sydney; Brauer, Michael et al. · 2022 · paperView source ↗verified through CrossrefAccessed on 9 September 2026.

It does not work if the water does not arrive. This is a failure mode that household intuition does not have on its map: an extreme-cold scenario could freeze shallow urban pipes and cut off supply at city scale, and there the filter does nothing ^[622]Frost depth increase under a nuclear winter scenario projected to sever piped-water access in the Northern HemisphereLamilla Cuellar, J. E.; Palm, R.; Denkenberger, David C. et al. · 2025 · paperView source ↗archived copy onlyAccessed on 9 September 2026. That is why the measure is two things: storing, and being able to treat.

Evidence. High on its own ground, with an honest caveat: it is measured in children in low- and middle-income countries with endemic diarrhoea, not in high-income households after an emergency. The mechanism is the same pathogen in the same water, so the transfer is plausible, but nobody has measured it.

Cost. Low. Rotated water containers and a filter or chlorine, in the quantities set out in the official guidance ^[956]Prepara tu Kit de EmergenciaServicio Nacional de Prevención y Respuesta ante Desastres · 2026 · official documentView source ↗Accessed on 9 September 2026.

What it does NOT solve. Nothing to do with AI, nothing systemic and nothing that lasts longer than your containers. It is a measure of hours to days, like everything in this block.