Our local water tower is empty during this winter storm.

I heard my water heater "running" even though there were no faucets on in the house - I immediately thought I had a burst pipe.

After finding no leaks, I turned on a faucet, and there was actually suction through the spout.

Because my home is on a hill, my theory is that other citizens running their water actually drained my house lines. Is this possible? Shouldn't there be backflow valves or something to prevent this?

In addition, should I be worried about my pipes freezing now that they appear to be empty?

Do standard "winter prep" rules apply to mostly drained plumbing?

I have 40 gallon tank electric heater. I have unplugged it since discovering there was no water.

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    There may or may not be backflow preventers installed; you'd have to ask your water supply company if that is standard at the road or locate one inside your home.
    – MonkeyZeus
    Commented Feb 17, 2021 at 19:49
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    If you open every tap in a drained system, the water will run out the lowest, emptying all the others. Empty pipes can't freeze, there's nothing left to freeze. Your "city" needs to sort this out, no-one here can. if your heating has back-drained (& it really shouldn't!) then you'll have to switch it off until supply is restored.
    – Tetsujin
    Commented Feb 17, 2021 at 19:49
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    @MonkeyZeus I have 40 gallon tank electric heater. I have unplugged it since discovering there was no water.
    – Aww_Geez
    Commented Feb 17, 2021 at 19:51
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    Many homes do not have back flow prevention only outside faucets and irrigation systems. I would put the water heater on pilot if gas and flip the breaker to off if electric. As far as flushing things I always suggest running an outside hose after a water interruption to get rid of all the sediment that was churned up when the lines recharge. Once the water is back and running clear it’s a good time to drain the water heater to clean the sludge out of it. I agree empty pipes won’t be a freezing problem what little water is left can expand as it freezes without breaking pipes.
    – Ed Beal
    Commented Feb 17, 2021 at 20:08
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    Interesting note: you can also experience this sort of reverse water pressure in the event of a fire in your neighborhood, when fire trucks are pumping large amounts of water through the hydrants.
    – bta
    Commented Feb 18, 2021 at 23:35

2 Answers 2


Yeah, it sounds like you got backsiphoned

Most houses in the US don't have any protection against their municipal water service going negative pressure and backsiphoning any garbage present at outlet points into them. Even if you have lawn irrigation, the vacuum breaker for that only prevents the irrigation system from contaminating things, not your whole water service. Likewise with hose bibbs; if your house is recent, your hose bibbs will have vacuum breakers on them, but many older houses lack these, so it was very possible that the contents of your neighbor's kiddie pool or garden sprayer got sucked into the water system. (Fortunately, most other domestic things have air gaps as part of their installation, but even those aren't foolproof due to the rise of fixtures with extensible heads.)

So, I'd turn off the water heater to avoid heating an empty tank, and make sure to flush your lines and faucets thoroughly once the water's back on, since there's no telling what could have been sucked in during the backsiphonage event. Also, listen to your water utility, as they may be putting out boil-water orders for a fair length of time after the water comes back on, or even telling you not to use it for drinking if something more...industrial has gotten into the works.


It should not be possible to fully drain your water tank unless you use the drain valve and tilt the unit. The lowest the water can go is the bottom of the cold water pipe. Notice the blue line I added to the image.

However if your heater is still heating then it could evaporate all of the water and cause premature death for your water heater. Notice both heating elements are above the minimum water line so you don't even need to drain all the water to kill your heating elements.

It would be wise to turn off your heater until utilities have been restored. There is no sense in wasting electricity to heat water which you cannot use especially during rolling blackouts.

Depending on how long you have stagnant water in your water heater then you should cycle out 50 gallons of water through your tank once services are restored or else you risk exposing yourself to legionnaires disease among other things. Before cycling out the water bring the temperature up to at least 140°F for a few hours, cycle the water out, and then bring the temperature back down.

I am not sure what you mean by "heard it running" but it could have been air passing through it via your aforementioned faucet suction.

If you can then turn off your main water supply line to prevent the backflow symptoms. If the water supply returns while you're not home then it could be catastrophic if you had an undetected pipe burst or if your home is below freezing temperature. Once water has been restored then slowly turn on your main supply and listen for potential leaks.

enter image description here

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    IPC includes a requirement for a vacuum breaker on water heaters, but it seems to be an "oft-overlooked" part of code.
    – Ecnerwal
    Commented Feb 18, 2021 at 14:20
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    Note that it's reasonably likely that when the water went out, the electricity went with it (OP will know). Therefore, if it's an electric heater, then it's not heating anything. However, it's still a good idea to flip the WH breaker off so that if power is restored before the water, the heater isn't burning itself up running empty. Of course, if it's gas (as shown in the image), the gas is still likely on, so it needs to be set to "vacation", "pilot", or just "off". (Source: my daughter is in TX right now and has been reporting power & H2O outages, either/or and simultaneous.)
    – FreeMan
    Commented Feb 18, 2021 at 14:42
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    @FreeMan Thanks! I've updated my image to an electric water heater and updated my answer slightly to reflect the anatomy.
    – MonkeyZeus
    Commented Feb 18, 2021 at 14:49
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    @FreeMan OP did mention that they unplugged the water heater at some point in the comments.
    – MonkeyZeus
    Commented Feb 18, 2021 at 15:02
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    @FreeMan Comments are second-hand citizens so if it's not in the post body then it's as good as being non-existent sometimes; especially in a 10+ comment thread.
    – MonkeyZeus
    Commented Feb 18, 2021 at 15:15

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