Hidden emergency water at home: water heater, toilet tank and pipes
Where to find water at home when the taps stop: the water heater, your pipes, the toilet tank, ice cubes and liquid in canned food. How to get it out safely and which water you must never drink.
In short
- A tank water heater holds 30–80 gallons (110–300 L), the biggest hidden water supply in most homes. You can drain it from the valve at the bottom after turning off its power or gas.
- Your pipes hold a few more gallons: open the highest faucet, then the lowest.
- Toilet tank water (not the bowl) is fine for washing and flushing; to drink, only if you don't use chemical tablets and you treat it.
- Never drink water from radiators, a boiler heating loop or a swimming pool.
When the tap runs dry, the first thought is the bottles in the pantry. But your home almost certainly holds dozens of gallons you’ve forgotten about: in the water heater, the pipes, the toilet tank. It doesn’t replace your water supply, but it can stretch it by several days.
How much you can find
| Source | Approximate amount | Drinkable? |
|---|---|---|
| Tank water heater | 30–80 gal (110–300 L) | Usually, after settling |
| Household pipes | 1–5 gal (5–20 L) | Yes, if the supply wasn’t contaminated |
| Toilet tank (not the bowl) | 1.5–3 gal (6–12 L) | Only without chemical tablets, and treated |
| Ice cubes in the freezer | a few quarts | Yes |
| Liquid in canned vegetables and fruit | a few cups | Yes |
| Pool, rain barrels | hundreds of gallons | Washing and flushing only |
| Radiators, heating loop | — | Never |
The water heater
- Turn off the power or gas to the heater. An empty heater left on can be damaged.
- Close the cold water inlet valve at the top.
- Let the water cool if it’s hot.
- Open a hot water faucet in the house so air can enter the tank.
- Open the drain valve at the bottom (attach a short hose if needed) and collect the water in a clean container.
- The first gallons may be cloudy: let them settle and use the clear water.
Find out now where your heater’s drain valve is and what container fits under it. Check the manual. Tankless heaters don’t store water.
The pipes
- If the supply may be contaminated, close the main shutoff valve.
- Open the highest faucet in the house (upstairs) to let air in.
- Open the lowest faucet (ground floor, basement or outside spigot) and collect the water.
The toilet tank
Water in the tank (the top part, not the bowl) is clean tap water. If you don’t use tablets or chemicals in the tank, you can drink it after boiling or treating it. Otherwise use it for washing or flushing.
For flushing and washing
To flush the toilet, use pool water, rain barrel water or used washing water. Pour 1–2 gallons straight into the bowl. See also hygiene without running water.
When to treat it
If you’re unsure about any source, boil, chlorinate or filter it before drinking. Water from radiators and heating loops can’t be made safe.
Prepare now
- Find your home’s main water shutoff and learn how to close it.
- Find your water heater’s drain valve.
- Keep a clean container and a short hose near the heater.
- Note how to shut off the water in your family plan.
- Keep a supply in containers: don’t rely only on hidden water.
Frequently asked questions
Is water heater water safe to drink?
Usually, if the heater is fed from a public supply and maintained. The first gallons may contain sediment and rust: let it settle and use the clear water on top. If in doubt, or if the supply was contaminated before it shut off, boil or treat it.
Should I close the main valve when the water goes off?
If authorities say the supply may be contaminated (after a flood or main break, for example), close your home's main shutoff so dirty water doesn't enter your pipes and water heater. That keeps the water already in your home clean.
Can I drink water from a hot water boiler or radiators?
Never. Water in a heating loop sits in pipes for years, contains rust and often chemical additives. Boiling or chlorine won't make it safe.
Sources and further reading
Preper is for general education and does not replace instructions from your local authorities or advice from a doctor. In an emergency, call your local emergency number.