Start Here
Four situations, four places to begin. Find the one that matches yours and skip the rest of the site until you need it.
Last updated August 28, 2026.
This site answers one question in about ninety seconds: if your tap stopped today, how long would your household last?
Everything else here exists to help you change that number. Where you should start depends on which of these four you are.
The tap is off right now
Skip the planning material.
Count what you already have in the building before you do anything else. Your water heater holds 40 to 50 gallons of drinkable water with a drain valve at the bottom. Every toilet tank holds a couple more. There is water in the pipes if you open the highest tap to break the vacuum and drain from the lowest.
For most houses that is 50 or 60 gallons you already own. Find it first, then work out how many days it buys you, then decide what to stop using.
If the water is running but you have been told not to drink it, boiling is the answer and you already own the equipment. Elevation changes how long you hold the boil.
You have never thought about this
Run the audit. It takes three questions and it will probably return a lower number than you expect.
That reaction is the entire point of the tool, and the fix is usually cheaper and simpler than people assume. Most households close a two-week gap for under $200, and a meaningful share of the fix costs nothing because the water is already in the house.
Once you have a number, the site tells you which direction to go. Short by a lot means storage. Short by a little means rationing. Short with nowhere to put containers means finding a way to produce water rather than keep it.
You already store water
Two questions worth checking.
When did you last rotate it? Water you bottled yourself needs replacing every six months, per CDC. Most people store water once, feel finished, and are still standing on that supply years later.
Are you counting the right daily figure? The one gallon per person per day rule that most plans are built on covers drinking and minimal sanitation only. No shower, no flush, no dishes. If you sized your supply on it and expect normal living, your real timeline is shorter than your label says.
You want to produce water, not just store it
Rain is the cheapest water you will ever collect. A thousand square feet of roof yields roughly 600 gallons from one inch of rainfall, which usually means storage is your limit rather than supply.
Check what your state allows first. Collecting rainwater is legal in every state, but several regulate volume or use, and the widely repeated claim that it is banned traces to a Colorado law that changed in 2016.
If you are considering an atmospheric water generator, work out its output at your actual humidity before you buy. The rated figure on the box assumes roughly 80% relative humidity. Below 40% these machines produce a fraction of that, and below 30% many produce almost nothing while drawing full power.
How to read this site
Every calculator shows its formula and names its source. Nothing is gated, nothing asks for an email before it gives you an answer, and every result includes what the method does not cover.
Where we think the honest answer is that you should not buy something, the tool says so. That includes the products this site earns commission on.
If a number here disagrees with CDC or your state health department, follow theirs, and tell us about the gap.