Need: 4 L (1 gal) per person per day minimum (2 L drinking, 2 L cooking/hygiene). Realistic comfort: 8–10 L.
Store first (Phase 0)
- Water bricks / stackable 15–20 L jerry cans (~£10-20 each) — fill from tap now, add 8 drops plain unscented bleach per gallon (2 drops per litre), rotate every 6–12 months. Target: 2 weeks minimum, 1 month better.
- Bathtub bladder (WaterBOB, ~£35) — 100 gal (~379 L), fill in 20 min the moment things look bad.
Rainwater harvesting (the renewable core)
- Maths: every 1 mm of rain on 1 m² of roof = ~0.9 L. A 100 m² roof in a 60 mm/month climate = ~5,400 L/month. More than a family needs.
- Budget build (~£100-250): rain barrel (55 gal (~208 L), £30-75, or a food-grade 220 L used barrel for £20-40) + downpipe diverter (£25) + first-flush diverter (£30 or DIY from PVC — the first 10–20 L of a rainfall carries roof filth; dump it) + mosquito mesh on every opening + spigot near the base.
- Step up (~£300-600): 275 gal (1,000 L) IBC tote — used food-grade ones go for £45-120. Paint it black-out (algae needs light) and elevate on cinder blocks for gravity pressure. Two totes = a month of buffer.
- Roof note: metal/tile roofs are best; avoid collecting from asphalt shingles for drinking if you can, or rely on filtration below.
Make ANY water safe — layered methods, cheapest to fanciest
Rule: filter (removes particles/protozoa/bacteria) then disinfect (kills viruses). For rainwater or clear stream water, one good filter is usually enough; for pond/floodwater do both.
- Boiling — the gold standard, costs only fuel. Rolling boil for 1 minute (3 min above 2,000 m altitude). Kills everything. Doesn't remove chemicals or mud — pre-filter through cloth.
- Gravity filters for base camp: Sawyer bucket adapter kit (£15-28 + any bucket) is the budget king. Platypus GravityWorks (£100-130) or a British Berkefeld stainless gravity filter (Doulton) with black elements (£180-280, elements also reduce chemicals) for household volume.
- Purification tablets (Aquatabs, ~£10/50) — featherweight backup for bags.
- SODIS (free): clear PET bottle, full sun, 6 hours (2 days if overcast) — UV kills pathogens. Slow but costs nothing; good for Phase 3.
- DIY biosand/charcoal filter (near-free): bucket or cut bottle layered top-to-bottom: cloth → gravel → coarse sand → fine sand → crushed charcoal from your fire → cloth. Improves clarity/taste and removes a lot of biology; still boil or bleach after.
- Solar still / transpiration bags (emergency only): pit + plastic sheet + centre stone dripping into a cup, or a clear bag tied over leafy (non-toxic) tree branches — yields are small (0.5–1 L/day) but it's distilled.