Water
How much water should a household store?
The numbers behind drinking, cooking and washing, how long stored water keeps, and how to make any fresh water safe to drink.
The numbers
There are three useful figures. An adult drinks around two to three litres a day in normal conditions, more in heat or with exertion. US emergency planners at Ready.gov advise storing at least one US gallon, about 3.8 litres, per person per day for drinking and basic sanitation. And the humanitarian Sphere standards, used by aid agencies worldwide, plan on around 15 litres per person per day once cooking and washing are included.
For a home kit, plan on 3 to 4 litres per person per day of drinking-quality water, and have a way to treat more for everything else.
For your household
| Household | 3 days | 7 days | 30 days |
|---|---|---|---|
| 2 people at 4 L/day | 24 L | 56 L | 240 L |
| 4 people at 4 L/day | 48 L | 112 L | 480 L |
| 6 people at 4 L/day | 72 L | 168 L | 720 L |
Beyond a few days, storing every litre stops being practical. That is when filtration matters more than storage.
Storing water
- Commercially sealed emergency water keeps for around five years. Store it cool and dark, away from chemicals and fuel.
- Tap water you bottle yourself should go into clean, food-grade containers and be replaced about every six months.
- Collapsible carriers take little space when empty and can be filled when a warning is issued.
- A bath reservoir, a sealed liner that sits in the bath, stores hundreds of litres of clean water if you fill it before supply stops.
Water already in your home
If your home has a hot-water cylinder, it holds a useful reserve that can be drained from the valve at the bottom once the heating is off and the water has cooled. A toilet cistern (not the bowl) holds several litres for washing or flushing. Water in a loft tank or a garden water butt is not safe to drink untreated, but becomes useful with a good filter and purification tablets.
Making water safe
- Boiling at a rolling boil kills bacteria, viruses and parasites. It needs fuel, so it suits small volumes.
- Hollow-fibre filters with 0.1-micron pores remove bacteria and protozoa, but not viruses. Use them on clear fresh water, and add tablets where sewage contamination is possible.
- Purification tablets treat a litre each; follow the contact time on the pack.
- Gravity filters with ceramic candles treat large volumes for a household over weeks without power.
Never drink water you suspect is contaminated with fuel or chemicals: filters and tablets do not remove them.