Keep faeces away from water and hands: the pit latrine and the handwashing station, then sewers that clean themselves and treatment instead of relocation.
Break the faecal–oral route on day one, before habits form.
Needs first: Find and hold water
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 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.
Level 0The 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 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 3The basic set from the WHO list: what each treats, what it is made from, and the earliest tier that can make it. No doses, on purpose.
Level 3Water in and on the ground, the air and weather, rocks and time, earthquakes and tsunamis, and the climate: each result with what it lets you do and who first found it.
Drawn overview sheets, each with its corrections printed under it. They orient; they are never the thing you identify from.
