Water

Filtering, storing, treating and finding water when the tap stops.

• Build a biosand filterA concrete or plastic column of sand that grows its own biological layer and cleans dirty water continuously. It removes almost all bacteria and protozoa, and only some viruses, so it never replaces boiling or bleach.
• Size and build a rainwater systemWork out what your own roof actually yields in a British year, then build the gutter, first-flush diverter and store that captures it. The maths is simple and the numbers are larger than most people expect.
• Make filter charcoal from your own fireCharcoal from a wood fire improves taste, smell and colour, and adsorbs some chemicals. It is not activated carbon, it does not disinfect, and used wrongly it makes water worse.
• Build a permanent slow sand filterThe Victorian municipal water technology, shrunk to a household. Bigger, slower and far higher capacity than a bucket biosand filter, and with the right maintenance it runs for decades.
• Solar still and transpiration bagBoth work. Both produce far less than the survival books imply, and in Britain a transpiration bag beats a ground still comfortably. Know the real numbers before you rely on either.
• Judge raw water before you treat itTwo minutes of looking, smelling and thinking about what is uphill will tell you more than any test kit you own. It also tells you which treatment will actually work.
• Improvise a distillation setupThe only method that removes salt, heavy metals and most chemicals. Slow, fuel-hungry, and the answer to problems where boiling and filtering both fail completely.
• Shock-chlorinate a tank or water buttHow to disinfect a contaminated store rather than throwing it away: the dose, the contact time, and the flush. One litre of ordinary 5% bleach per 1,000 litres gives you 50 ppm.
• Reuse greywater safelyBath, shower and laundry water can halve your fresh water demand. Kitchen water is a different substance and is not in this category. And untreated greywater must never be stored.
• Test and disinfect a well or boreholeA private supply is the best water asset a household can have and the easiest to quietly poison. How to work out the volume, dose it, circulate it and flush it, and what testing actually tells you.
• Melt snow and ice for waterSnow is mostly air, so it yields far less water and burns far more fuel than people expect. Ice is worth roughly three times as much. Never eat snow to quench thirst.
• Look after a squeeze filterBackflushing, and the one failure mode that matters: freezing splits the fibres, cannot be seen, cannot be tested at home, and leaves a filter that still flows normally while passing everything through.
• Build a gravity bucket filterTwo stacked buckets and a filter element give you clean water on tap with no pumping, no squeezing and no power. The easiest genuinely useful thing on this list to build.
• Read UK water risks: algae, runoff and saltThe three contamination risks specific to British water, and the one where boiling makes it worse rather than better.
• Fill and manage an emergency bath storeThe 300 litres you can capture in the ten minutes before the mains goes off, and the honest truth about how long a bath of water stays drinkable.