How much water to store, and how to actually store it

Water is the first thing you run out of and the cheapest thing to get right. It is also the one where the standard advice quietly under-serves you, because the number almost everyone repeats was written for evacuation, not for staying home.

How much water does one person need per day?

One gallon per person per day. That figure comes from Ready.gov and it covers drinking plus a small allowance for basic hygiene and food preparation. It is not a drinking-only number, which is why it looks generous next to the two litres a day you might see quoted elsewhere.

Two adjustments matter:

• Hot climates, illness, pregnancy and nursing all push the number up. Ready.gov says so explicitly and does not give a multiplier, which is fair, because the honest answer is "more, and you will know."
• Pets need their own allowance. A 50-pound dog drinks roughly half a gallon a day. Nobody puts this on a kit list and everybody has a dog.

Three days or two weeks?

Three days is the evacuation number. It answers the question "what do I carry out of the house," and for that it is correct.

Two weeks is the sheltering number, and it is the one most households actually need. Ready.gov itself recommends a two-week supply at home where storage allows. Extended outages after hurricanes, ice storms and wildfire-driven power shutoffs routinely run past a week, and a boil order can outlast the outage that caused it by several days.

The gap between those two numbers is the single biggest gap in most people's plans.

Here is what it costs in physical terms, which is the part that decides whether it happens:

Water weighs 8.34 pounds per gallon. That puts a full 7-gallon jug at about 58 pounds of water, over 60 once you count the container. It is right at the edge of what one adult carries comfortably, and well past what anyone wants to carry down basement stairs twice.

Before you buy anything, go and look at where it will live, and measure the shelf. A two-week supply for four people is eight of those jugs. The question is not whether you have room for the volume, it is whether the surface holding them is rated for five hundred pounds. Most garage shelving is not, and the failure mode is a flooded garage rather than a dry one.

What should I store it in?

Three tiers, cheapest first.

Free or nearly free. Commercially bottled water, bought at the grocery store. It is already sealed, already potable, needs no treatment, and its date is printed on it. Buy a case a week for a month and you are done. This is the correct answer for most households and it gets skipped because it is boring.

Sensible. Food-grade water containers in the 3.5 to 7 gallon range, filled from the tap. Rigid, stackable, with a spigot or a vent cap. Fill them, date them with a marker, and replace the water every six months. Larger is not better here: a 15-gallon drum weighs 125 pounds and you will not move it, which means you need a pump or a siphon, which is one more thing to fail.

Overkill. A 55-gallon drum with a bung wrench and a siphon pump, or a plumbed rainwater system. Genuinely appropriate for rural properties on wells, where a power cut also stops the pump. Overkill for a suburban house that can refill from a neighbour's tap.

Do not store water in containers that held milk or fruit juice. The residual sugars and proteins are impossible to fully remove and they feed bacterial growth. Old bleach bottles are also out. Both of these appear on preparedness lists constantly and both are wrong.

What most water guides get wrong

They stop at "one gallon per person per day" and never convert it to weight or floor space. Volume does not tell you whether the plan is possible. Weight and footprint do. A plan that requires 467 pounds of water on a shelf that holds 200 is not a plan.

They treat filtering and disinfecting as the same job. They are not. A backpacking filter removes protozoa and bacteria and does nothing to viruses or dissolved chemicals. Chemical disinfection handles viruses and bacteria well and is unreliable against cryptosporidium. Boiling handles all three biological categories and nothing chemical. The EPA's emergency disinfection guidance is direct about these limits, and the practical answer is to boil when you can and treat when you cannot.

They publish a bleach ratio from memory. Household bleach is sold at several concentrations, and the correct number of drops per gallon depends on which one you have. Getting this wrong in either direction is bad. Read the current CDC table at the time you need it, and keep the bottle's label rather than a scrap of paper with a number on it.

They never mention the water already in your house. A conventional water heater holds 40 to 50 gallons. That is a two-week supply for two people, sitting in your basement right now. It needs the power or gas off, the inlet valve closed, and a hose on the drain valve at the bottom, and the first gallon will be full of sediment. Toilet tanks, not bowls, hold another few gallons of clean water each.

How do I make questionable water safe?

Boiling first, because it is the most reliable and needs no supplies you do not already own.

Bring water to a rolling boil and hold it there for one full minute. Above 6,500 feet, make it three minutes, because the boiling point drops with altitude and one minute is no longer enough. Let it cool, and pour it between two clean containers to put some air back into it if the flat taste bothers you.

If the water is cloudy, filter it through a coffee filter or a clean cloth and let it settle before you boil or treat it. Suspended solids protect microorganisms from chemical disinfection and give them somewhere to hide.

Chemical disinfection is the fallback when there is no heat source. It works on bacteria and viruses. It is not dependable against cryptosporidium, which is exactly what you get from surface water contaminated with animal waste, so it is a second choice rather than an equal one.

The 20-minute version

If you do nothing else this week:

1. Count the people and pets in your house and multiply by 14. That is your gallon target.
2. Buy that many gallons of commercially bottled water over the next month. Put them somewhere out of sunlight and off a concrete floor.
3. Find your water heater's drain valve and confirm a garden hose threads onto it. Do this now, not during an outage, with a torch in your teeth.
4. Put the CDC disinfection page in your phone's offline reading list, and print one copy for the folder with your other documents.

That is the whole first pass. It costs about the price of a takeaway, it takes one Saturday of attention spread across a month of shopping trips, and it moves you from three days to two weeks.