Emergency Water in Your Home: How to Drain a Water Heater and Which Indoor Sources Are Safe

Most people looking for emergency water sources in your home go straight outside, to the creek or the rain barrel. Meanwhile there are 40 to 80 gallons of clean, already-treated drinking water sitting in a steel tank in the garage, and another few gallons in the pipes running through the walls. It's the most overlooked supply in preparedness, and it's free.

Timing makes this worth reading now. The National Hurricane Center puts the peak of the Atlantic hurricane season at September 10, "with most activity occurring between mid-August and mid-October." That's the window when boil advisories and multi-day outages cluster. So let me walk you through what is in the house, how to get it out safely, and what to leave alone.

How much drinking water is already inside your house?

More than you think, and almost all of it is water your utility already treated. The three pools of it are the water heater, the supply pipes, and the toilet tanks.

• Water heater tank. Most residential tanks run 40 to 80 gallons. Colorado State University Extension, in its guidance on emergency water supplies and treatment, says "Hot-water tanks are the best source of indoor water because they hold an average of fifty gallons of water."

• Supply pipes. Usually a few gallons in an average house, more in a large one with long runs.

• Toilet tanks. Roughly 1.6 gallons in a modern tank, up to 3.5 gallons or more in an older one. Multiply by the number of bathrooms.

Put that against the planning number. CDC's guidance on creating and storing an emergency water supply is "at least 1 gallon of water per person, per day for 3 days," and it adds "Try to store a 2-week supply if possible." A 50 gallon water heater alone covers a family of 4 for roughly 12 days of drinking and basic sanitation. That's not a footnote. That's the plan. If you haven't worked out how much water to store per person in your household yet, do that first and count the tank as part of the total.

How do you safely drain a water heater for drinking water?

Shut off the heat source first, then break the vacuum, then drain. Do it in the wrong order and you either burn out a heating element or scald yourself. Here's the sequence.

1. Kill the heat source. On a gas unit, A.O. Smith's own instructions are to "Turn the control knob to the 'off' position," turn off the electrical supply to the unit, and then "Close the valve by turning the handle so it's at a right angle to the gas line." On an electric unit, go to the panel: "many water heaters have two circuit breakers, and some use a 240-volt supply. Both circuit breakers must be shut off."

2. Let it cool. A tank at a normal setting holds water hot enough to scald in seconds. CSU Extension's warning is blunt: "Remember, the water coming from the tank can be scalding hot." Give it a few hours if you can, and wear gloves either way. A.O. Smith recommends "heavy gloves to protect yourself."

3. Close the cold water inlet. That's the valve on the cold line coming into the top of the tank. This isolates the tank from the street. If your utility has issued an advisory, or if pressure has dropped, this step also keeps contaminated water from being pulled into the tank.

4. Open a hot water faucet somewhere in the house. This is the step people skip, and then wonder why nothing comes out of the drain. CSU Extension explains it: opening a hot tap "provides a vent so that water can flow from the tank." Without air coming in the top, the vacuum holds the water in.

5. Drain into clean containers. Thread a short garden hose onto the drain valve at the bottom of the tank, or set a clean pail underneath. CSU Extension says to "Place a clean pail or bucket under the drain at the bottom of the tank to retrieve the water."

The sediment reality nobody mentions. The first gallon or two out of a tank that has never been flushed will be rusty, cloudy, and full of mineral grit that settled at the bottom. That's normal. Let it run into a bucket you're going to dump, then start collecting once it runs clear. If it never runs clear, filter the sediment out through a clean cloth or coffee filter and then disinfect. Also expect the drain valve on an old heater to weep afterward. Plastic valves in particular can fail to reseal, so know where your main shutoff is before you touch it.

Refilling afterward. Reverse the order, and one step is non-negotiable on an electric heater. A.O. Smith puts it this way: "For an electric water heater, it is critical to make sure the tank is full before turning the power back on. If there is not enough hot water around the heating element, it will burn out." Fill the tank completely, open a hot tap until it runs steady with no sputtering, and only then restore power or gas. CSU Extension gives the same order: turn the intake valve on, let the tank fill, and only then should "the gas or electric be turned on."

When should you not drain your water heater?

There are four situations where you stop and do something else instead.

• You smell gas. Do not touch the gas valve, do not flip a light switch, do not use a phone inside. Get everyone out, and call the gas utility's emergency line or 911 from outside. A gas smell is not a plumbing problem, it's an evacuation.

• The tank is still hot and you need water now. Scalding is the single most common injury in this job. If you can't wait for it to cool, drain slowly into a metal pot rather than a plastic jug, wear heavy gloves and closed shoes, and keep children and pets out of the room.

• Water is already flowing backward. If the house lost pressure and there's any chance of backflow, meaning contaminated water being siphoned back into your plumbing, close the main shutoff to the house before you draw anything. Oregon State University Extension's water storage guidance says it plainly: "If there have been warnings that the public water supply isn't safe, turn off the water to your house before using these sources to prevent contamination."

• The water came from a flooded area. If flood water has reached the utility room or come up through a basement drain, that tank water is suspect. CSU Extension notes that flood water "could be contaminated with sewage, oils, industrial, and/or hazardous wastes." Boiling and filtering will not fix fuel or solvents.

How do you get the water out of your supply pipes?

Let gravity do it. Open the highest faucet in the house first, which lets air into the system, then collect from the lowest faucet in the house, usually a basement sink or an outdoor spigot. CSU Extension describes exactly this: open the highest faucet, then draw the water from the lowest one.

Two things worth knowing before you do it:

• Close the main shutoff to the house first if there's any question about the street supply. If you don't know where it is, take ten minutes today and find your gas, water and electric shutoffs. Otherwise you're just draining the city main through your kitchen.

• If your home has lead solder or lead service lines, the water that has been sitting in those pipes is the worst water in the house, not the best. Flush and use it for washing, not drinking, and use your stored water or the heater tank for consumption.

Is toilet tank water safe to drink?

The tank can be, the bowl never is. CDC's list of safe indoor water sources includes "Water from your home's toilet tank (not from the bowl), if it is clear and has not been chemically treated with toilet cleaners."

Read that condition carefully, because it disqualifies a lot of American bathrooms:

• No blue or colored cleaning tablet in the tank, ever. Those tablets are usually chlorine plus dyes and surfactants that were never meant to be swallowed.

• No automatic bowl cleaner cartridge that feeds from the tank.

• The water has to be clear. A tank with a rusty flapper, mineral scale, or a biofilm ring is not a source you want.

Even when it passes all three tests, treat it. Boil it or disinfect it. Tank water sits open to room air for months and the tank itself is not a food-grade container, and if you plan to run it through gear instead, it's worth knowing the difference between a water filter and a water purifier first.

What other indoor sources are safe?

Two more, both easy to forget. CDC lists "Melted ice cubes made with water that was not contaminated" and "Liquid from canned fruit and vegetables."

Ice. A full freezer's ice maker bin plus the trays is often 5 to 10 pounds of water, and roughly a pint per pound. During an outage, that ice is doing double duty keeping your food cold, so let it melt in a covered container inside the freezer and collect it as it goes rather than pulling it out early.

Canned vegetable and fruit liquid. A standard 15 ounce can holds several ounces of liquid. It's salty in the case of vegetables and sugary in the case of fruit, so it's not a substitute for plain water, but it's calories and fluid and it's already sterile inside a sealed can. Drain it into a cup instead of down the sink.

One caution on salt. Very salty liquid makes dehydration worse, not better, if that's all you're drinking. Use canned liquid to stretch a supply, not to replace it.

Which indoor water sources are not safe to drink?

This list matters more than the safe list, because these are the ones that look like water and are not.

• Swimming pools and spas. CDC is direct: pool and spa water "can be used for personal hygiene, cleaning, and related uses, but not for drinking." The reason is chemistry. Pool water carries stabilizer, algaecide, clarifier, and pH adjusters, and CDC's home pool and hot tub guidance describes running pools at 1 ppm free chlorine, or at least 2 ppm when cyanuric acid is present. Cyanuric acid is the stabilizer, it accumulates because it does not evaporate or break down, and it's not something you filter out with a camp filter. Boiling concentrates it further.

• Hot tubs. Worse than pools. CDC recommends at least 3 ppm chlorine in hot tubs, the water is warm and biologically active, and the plumbing holds biofilm you can't see. Wash with it. Do not drink it.

• Water beds. The vinyl bladders are treated with algaecides and plasticizers, and most owners have added a conditioner chemical at some point. Use water bed water to flush toilets, nothing else.

• Radiators and boiler systems. CDC specifically warns against using the home heating system tank in older homes, as distinct from the tap water heater. Closed hydronic loops routinely contain rust inhibitors, glycol antifreeze, and dissolved metals from decades of circulation.

• The toilet bowl. Not for drinking, not for washing dishes, not for anything but flushing, and that includes bowls that look clean.

• Anything that came from flood water. Ready.gov's flood guidance is to avoid wading in it at all, and warns that "Underground or downed power lines can also electrically charge the water."

What should you do the moment you hear a boil advisory is coming?

Fill everything while you still have pressure. Advisories and outages usually give you some warning, whether that's a storm track, a utility text, or the sound of a main break down the street. You have minutes to hours, and water that's already in your house is water you do not have to treat. Reading up on what a boil water advisory means for your household before one lands saves you the scramble later.

In rough priority order:

1. Drinking containers first. Sanitized jugs, pitchers, clean pots with lids. This is the water you'll actually consume, so it gets the cleanest vessels.

2. Every cooking pot you own. Stockpots, Dutch ovens, the coffee carafe. Cover them.

3. The bathtub. A standard tub holds roughly 40 to 60 gallons. Scrub it first, because tub surfaces are not clean, and understand that this is flushing and washing water, not drinking water, unless you treat it. A cheap tub liner bladder solves the cleanliness problem if you keep one in the closet.

4. The washing machine. Run it to fill and then stop the cycle. That's another 15 to 30 gallons of gray water for flushing toilets.

5. Then the heater tank stays untouched. Close the cold inlet so it holds clean pre-advisory water, and leave it as your reserve.

Once the advisory is in force, CDC's boil water advisory instruction is to "Bring clear water to a rolling boil for 1 minute. At elevations above 6,500 feet, boil water for 3 minutes." One note on that threshold: EPA's emergency disinfection guidance sets the same 3 minute rule at 5,000 feet instead. The two agencies disagree. If you live at altitude, use the more conservative number and boil for 3 minutes.

And the limit that catches people out: CDC states "Boiling does NOT remove chemicals." If your utility says the problem is chemical rather than microbial, boiling makes it worse by concentrating it. Use bottled water and follow what your utility tells you.

How do you sanitize containers before you fill them?

Bleach solution, 30 seconds of contact, then rinse or air dry. CDC's method is specific: mix "1 teaspoon of unscented liquid household chlorine bleach in 1 quart (4 cups) of water" using bleach with 5 to 9 percent sodium hypochlorite. Cover the container and shake it so the solution touches every interior surface. Then "Wait at least 30 seconds and then pour the sanitizing solution out."

A few practical notes from doing this:

• Use unscented bleach only. Scented, splashless and color-safe bleaches contain additives that do not belong in a drinking container.

• Do not skip the lid and the threads. That's where the contamination lives.

• Never reuse a container that held milk, juice, or anything non-food. Sugars and proteins soak into the plastic and feed bacteria no matter how you wash it.

• If you're storing tap water rather than using it right away, CDC says to "replace the water every 6 months."

If you need to disinfect the water itself rather than the container, CDC's household bleach ratio is 8 drops of 5 to 9 percent bleach per gallon, or 40 drops per 5 gallons, then let it stand 30 minutes.

When should you get help?

Call 911 if someone is scalded badly enough to have blistering over a large area, if anyone collapses, or if you smell gas and can't get everyone out safely. For a gas smell with everyone already outside, call the gas utility's emergency number from a safe distance.

If someone swallowed pool water, water bed water, radiator fluid, or water that had a cleaning tablet in it, call Poison Control at 1-800-222-1222. They answer 24 hours a day and they will tell you whether it's a watch-and-wait or an emergency room trip. Do not make anyone vomit unless Poison Control tells you to.

Call a healthcare provider for diarrhea that lasts more than a couple of days after drinking questionable water, for blood in the stool, for a high fever, or for signs of dehydration such as very little urine, dizziness when standing, or confusion. Move faster than that for a young child, an older adult, or anyone with a weakened immune system.

Frequently asked questions about emergency water sources in your home

How many gallons of water are in a home water heater?

Most residential tanks hold 40 to 80 gallons, and Colorado State University Extension puts the average at 50 gallons. At CDC's planning rate of 1 gallon per person per day, a 50 gallon tank covers a family of 4 for about 12 days of drinking and basic sanitation.

Do I have to turn off the gas before draining a water heater?

Yes. Turn the gas control knob to off and close the gas supply valve before you drain, or shut off both breakers on an electric unit. A tank running dry with the burner or element still energized damages the heater, and on an electric unit A.O. Smith warns the upper heating element will burn out.

Can I drink water from my toilet tank?

Only if it's clear and has never had a cleaning tablet, drop-in cleaner, or bowl cartridge in it, and only after you boil or disinfect it. CDC allows toilet tank water on that condition and specifically excludes the bowl. If you can't remember whether a tablet was ever used in that tank, do not drink it.

Is swimming pool water safe to drink in an emergency?

No. CDC says pool and spa water can be used for personal hygiene and cleaning "but not for drinking." Pool water carries cyanuric acid stabilizer, algaecides and other additives that ordinary filters do not remove and that boiling concentrates rather than eliminates. Use it for flushing toilets and washing, and drink from your stored water or your water heater.

Should I fill the bathtub before a storm?

Yes, and do it before the pressure drops rather than after. A standard tub holds roughly 40 to 60 gallons, which handles toilet flushing and washing for several days. Scrub the tub first, and treat that water as non-drinking unless you boil or disinfect it. A tub liner bladder is a cheap upgrade if you keep one on hand.

How long can I store the water I drained from my water heater?

Treat it like any stored tap water. CDC's guidance for water you fill yourself is to replace it every 6 months, and to keep it in sanitized food-grade containers, sealed, in a cool dark place away from gasoline, solvents and pesticides. If it was cloudy or rusty coming out of the tank, filter and disinfect it before you store it, not after.

You never know, but you can always be ready.

Sources: CDC, How to Find Clean Water in an Emergency, CDC, How to Create and Store an Emergency Water Supply, CDC, How to Make Water Safe in an Emergency, CDC, Boil Water Advisory, CDC, Home Pool and Hot Tub Water Treatment and Testing, EPA, Emergency Disinfection of Drinking Water, Colorado State University Extension, Emergency Water Supplies and Treatment, Oregon State University Extension, Water Storage for Emergencies, A.O. Smith, How to Turn a Water Heater On and Off, Ready.gov, Build a Kit, Ready.gov, Floods, NOAA National Hurricane Center, Tropical Cyclone Climatology.