Clarify, then disinfect: boiling, sunlight, chlorine and slow sand, up to a treatment works that measures what it does.
Kill what is in the water before it kills you.
Needs first: Find and hold water, Fire, and keeping it (Energy)
Choose by what you have. Tick what is on or near the site. The options you can build move to the top; nothing is hidden.
Nothing ticked: every option is shown in the site's order.
A rolling boil for 1 minute, 3 minutes above 2,000 m. Nothing to measure and nothing to get wrong.
Clear PET bottles under 3 litres, 6 hours in full sun. Clear water only.
Two drops of 5% unscented bleach per litre of clear water, then 30 minutes before drinking.
The only method that scales. Needs 2–3 weeks to ripen before it protects anyone.
Make sodium hypochlorite from salt, water and direct current, measure its strength, and dose drinking water so that 0.2–0.5 mg/L of free chlorine remains 30 minutes later.
Needs first: Make water safe, Salt (Materials), Batteries: from the voltaic pile to the lead-acid cell (Energy), Glass (Materials)
Cross-listed. Its home is Water & Sanitation › Sanitation.
Keep a dense settlement from poisoning itself.
Needs first: Cement and concrete (Materials), Blast furnace and cheap iron (Materials), Germ theory and antisepsis (Health), The factory and interchangeable parts (Tools), Make chlorine disinfectant
Every guide, build, reference sheet and book reached from the steps above.
The thing that kills first, and the one problem on this site that is completely solved — provided you do it every single day, including the day everyone is exhausted.
Level 0Making fire once is a trick. Never having to make it from nothing again is the skill, and the difference between them is tinder you collected yesterday.
Level 3The two dozen that decide who lives where there is no doctor: what each does, how it spreads, what kills it and which step stops it.
Level 1The poisonings a rebuilding community is most likely to meet: where each comes from, how it shows, and the first thing to do.
Level 5Radio, heat, light, ultraviolet and X-rays are one thing at different wavelengths: what each band does, and the radio bands by name.
Level 3What matter is made of and how it changes: amounts, gases, acids, the energy and speed of reactions, electrochemistry, and the reactions every industry on the ladder runs on.
Level 0The distance between a latrine and a well, a bar of soap, and a covered pit prevent more deaths than every hospital on the ladder combined.
Drawn overview sheets, each with its corrections printed under it. They orient; they are never the thing you identify from.
