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Survival · Water

How to find and purify water when you cannot trust the tap

Field methods for finding, purifying, and storing water: boiling, filters, chemicals, and solar stills. Titles from 806 offline guides. The full protocols stay in the app.

§ 01

The direct answer

You need about 3 litres of drinking water per person per day at rest in a temperate climate, and 4 litres or more if you are walking, clearing debris, or in heat. That number fails before food does. Treat every untreated source as contaminated: surface water, rain off a dirty roof, melted snow, and well water after flooding.

Four methods cover almost every field case. Boiling: a rolling boil for 1 minute at sea level, 3 minutes above 2,000 m, kills pathogens. Filtration: a 0.1-0.3 micron filter removes protozoa and most bacteria; it does not remove viruses unless the filter is rated for them. Chemicals: unscented household bleach at ~2 drops per litre (5-6% sodium hypochlorite), 30 minutes wait, or iodine tablets per the packet. Solar stills and condensation: slow, low-volume, useful when no fuel and no tablets remain.

Order of work: settle sediment, filter or cloth-strain, then disinfect. Cloudy water wastes chemical dose and clogs filters. Do not drink seawater, urine, or blood. They raise the water you owe. The app holds 413 water articles behind this page: desert seeps, tropical vines, raft stills, CERT storage. Titles below. Protocols stay offline.

§ 02

Method comparison: one decision table

Pick the method you can actually run with what you have. Time and kill-range matter more than preference.

Boiling
Kills bacteria, viruses, protozoa. Needs fuel + pot. 1 min rolling boil (3 min above 2,000 m).
0.1-0.3 µm filter
Protozoa + most bacteria. Fast. Viruses usually pass unless the filter says otherwise.
Bleach / chlorine
~2 drops unscented 5-6% bleach per litre; 30 min. Weak on some cysts (Crypto).
Iodine tablets
Follow the packet. Not for long-term use or pregnancy. Taste is a feature. It means dose happened.
Solar still
Low yield (often <0.5 L / still / day). Last resort when you have sun, a pit, and plastic.
§ 03

In the offline library: titles only

12 titles · 806 articles in this cluster · full text in-app

  1. 01Water Storage and Purification for Emergencies: CERT-Recommended Methods
  2. 02Finding Safe Water in the Tropics: Animal Signs and Natural Indicators
  3. 03Desert Water Sources: Identifying and Evaluating Potential Supplies
  4. 04Water Procurement at Sea: Rain, Dew, Solar Stills, and Desalting Kits
  5. 05Constructing a Belowground Solar Still: Step-by-Step Instructions
  6. 06Building an Aboveground Solar Still: Collecting Water from Plants
  7. 07Using Polluted or Salt Water in a Solar Still: Safe Water from Unsafe Sources
  8. 08Solar Still and Condensation Techniques for Water Collection in the Jungle
  9. 09Improvising Water Containers in the Wild: Step-by-Step Guide
  10. 10Extracting Water from Vines, Roots, and Palms: Safe Methods and Dangers
  11. 11Avoiding Poisonous Plants When Building a Solar Still
  12. 12Hot Weather Sea Survival: Sun Protection and Hydration Strategies

Titles only. Full text, regional variants, and tables are in the offline library. They are not published on this site.

§ 04

Related

Rationing calculator →Fire →Offline library →

All eighteen topics: survival index. Educational reference: disclaimer.

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You’re reading this with a signal. The situation it describes is one where you won’t have one.