Most preparedness advice starts with what to buy. This is the free version, and it costs nothing.

If your municipal water goes down tomorrow, your household already has 40 to 60 gallons of clean water sitting inside the building. Almost nobody knows where it is, and by the time they need it they have usually already drained it.

Your water heater holds 40 to 50 gallons.

Kill its power or gas first and let it cool. Open a hot tap upstairs to break the vacuum, then draw from the drain valve at the base into clean containers. Expect sediment in the first flow. That is one tank, one household, several days of drinking water.

Your toilet tanks hold about 3 gallons each. The tank, not the bowl — and only if you have never used in-tank chemical cleaner tablets.

Your pipes hold several gallons. Open the highest tap in the house to let air in, collect from the lowest.

Here is the part that decides whether you get any of it: shut off your incoming water main early. That traps clean water in your system instead of letting it drain back out or be displaced by contaminated supply. If you wait until you are thirsty, the decision has already been made for you.

Go and find your main shutoff this week. Most people cannot tell you where theirs is. It is usually where the supply line enters the building — basement, crawlspace, utility room, or an exterior box. Tag it. Show everyone in the house.

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One correction while I am here, because it is the most dangerous myth in this space.

The DIY sand-and-charcoal bottle filter you have seen in a hundred videos does not make water safe to drink. It removes sediment, cloudiness and some chemicals. It does not reliably remove bacteria, viruses or protozoa. It is a pre-filter. You still have to boil it for a full minute at a rolling boil, or treat it with 8 drops of plain unscented bleach per gallon and wait 30 minutes.

People have made themselves seriously ill trusting that filter on its own.

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None of this is about predicting a collapse. Nobody can do that, and the people who keep trying eventually lose credibility for it. It is about reducing the number of ordinary, boring things — a storm, a grid fault, a burst main, a two-week outage — that can take a household from comfortable to desperate.

One gallon per person per day. Two weeks stored. Know your shutoffs. Have a way to treat water that needs no power and no fuel.

That is a weekend of work and it puts you ahead of essentially everyone on your street.