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We recently sold our home and per inspector had a licensed plumber install a new expansion tank. We moved out, but continued to visit the home to clean, so we know there is no water on and no leaking toilet. We just received our final bill saying we used almost 250,000...yes, 250,000 gallons of water in 8 days!! When we were not even using the water daily. Not sure if the new expansion tank could be faulty or any other explanation would be helpful. We had the meter re-read and the actual reading is correct. Thanks!

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    Is the new expansion tank 250,000 gallons? Imagine if you used that much water in 8 days, your house would be floating away. If your pipe from the city is 1 inch with average flow, then it would take 4.6 days with that pipe wide open(cut). Think something screwy is going on.
    – crip659
    Sep 6, 2022 at 22:48
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    There are 86400 seconds in a day, and about 250,000 seconds in 3 days. Therefore you are using 0.4 gallons per second or 25 GPM. I seriously doubt a 3/4" main feed pipe could even supply that. This data can't be right. Sep 6, 2022 at 23:21
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    Perhaps your neighbors recently installed a new Olympic-sized swimming pool? If so, good news, it is almost half full now! Sep 7, 2022 at 15:35
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    Would you mind posting a picture of the bill, after covering all identifying information? I'd really love to see this.
    – jay613
    Sep 7, 2022 at 17:37
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    Please update when you find out; I'm fascinated to learn the resolution of this. Sep 8, 2022 at 19:50

4 Answers 4

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No, a new expansion tank could not cause this.

A pipe or valve being broken during the repair could cause a leak, and a leak on your side of the water meter could cause a lot of water to be used, but a quarter million gallons is a lot of water!

A possible explanation is that your water company hasn't been reading your meter faithfully and has instead been estimating your water usage. Now that they've made a "final" reading of the meter, the current meter reading may show just how far off their estimate was.

If this is the case you may really have used all of that water, but over the last X number of months/years, not 8 days. If that is the case, I guess it's up to you how much you can push back against the bill for them being negligent or not billing you in a timely manner, but that's a different question... ;)

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    This could very well be right but holy moly is that negligent. My bill has a "previous" and "current" field. They read the meter every other bill so "current" will have either "(estimated)" or "(actual)" affixed to it.
    – MonkeyZeus
    Sep 7, 2022 at 11:58
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    Might also be a meter misreading. It happens.
    – ceejayoz
    Sep 7, 2022 at 14:11
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    @ceejayoz, you are spot on. If I were the OP, I would ask the utility to please re-confirm the meter reading and ask if it seems reasonable that I used so much water in so little time. A few years back my uncle got a natural gas bill for $25,000+. He asked the utility if it was even possible for his meter to handle that much flow in a month. Things got sorted out after that.
    – spuck
    Sep 7, 2022 at 15:01
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    This happened to me with my natural gas meter. It should be illegal for these companies to estimate your bill... in my case the rep said "oh ya, looks like the meter reported a malfunction in october of last year" which was 9 months ago. Why the heck did they not send someone out for 9 months to fix it!?
    – SnakeDoc
    Sep 7, 2022 at 16:18
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    @DeanMacGregor Well, around here they have the smart meters, so it phones home for readings, and phones home when it thinks there's trouble. In my case the gas company agent was able to tell me the exact date it reported trouble... and it was 9 months prior... and nobody had been dispatched to deal with it. Which meant I had been paying a fake bill for 9 months. Brilliant... I say illegal because 9 months is excessive.. .and then they tell you "btw you now owe us $X and you have no way to prove otherwise so pay up or else..." - really scummy.
    – SnakeDoc
    Sep 7, 2022 at 17:21
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In this answer, I'm assuming that your meter was previously read within the two months before your last bill, and that this discrepancy isn't a difference between estimated and actual usage that accumulated over years. It's not clear how you established this usage was billed over 8 days; it sounds like that's the time between the expansion tank installation and the next billing date, but since you didn't look at the meter when the tank was installed, that might be wrong.

I think it's hard to comprehend the amount of water we are talking about here. It's 3/4 acre-feet, enough to cover an acre with 9 inches, or a quarter-acre with 3 feet of water! 250,000 gallons is more water than my family uses in two years.

Wherever you live, I'd be somewhat surprised that a spike in demand equivalent to one hundred homes popping into existence would go unnoticed and unquestioned by both your water supplier and water treatment facility.

I would explain to the water company that it's not physically possible for them to supply water at that rate, and ask for your bill to be corrected. They might want to test or simply replace your meter. If they balk, ask them to find the leak and where the water is going. That is, nicely ask them to provide evidence of your consumption other than your meter, like water meter logs upstream and downstream of your home.


Regarding the expansion tank: an expansion tank is like a bottle; it has only one opening. At the bottom of the tank is a bladder filled with air. As cold water fills your water heater and is heated, it expands a tiny bit. Water is effectively incompressible, so that hot water needs more space. Rather than letting the pressure rise so much that all of your pipes stretch repeatedly and eventually break, the air bladder in the expansion tank is compressed. The small amount of water that enters the tank is pushed back out when the pressure drops.

The only path from from the expansion tank to the sewer is through the rest of your plumbing. Unless there's a visible leak from the tank, its net consumption of water is zero.

Unless the tank is flooding your home, it can't be responsible.

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    What do you think about the expansion tank? That's what the OP is asking about.
    – JACK
    Sep 7, 2022 at 17:40
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    I'd be somewhat surprised that a spike in demand equivalent to one hundred homes popping into existence would go unnoticed and unquestioned by both your water supplier and water treatment facility. THIS. I once had a toilet whose flapper valve was failing. I procrastinated it for maybe a month as it worsened "okay, this weekend we'll fix this." I got a visit from techs saying they were gonna shut off my main if I'd not been there to answer the door. I was probably using an extra few gallons per hour--they notice.
    – zedmelon
    Sep 8, 2022 at 20:36
  • My water company is a bit more easygoing, but at least as attentive. No one came to my door, but the company once notified me by letter that I probably had a slow leak at a toilet or other fixture, based on monitoring my water usage pattern (I guess at a pretty fine-grained level). And they were right: I had a leaky fill valve in one of my toilet tanks.
    – PellMel
    Sep 9, 2022 at 22:25
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If you don't have a check valve after the meter then you could get fluctuations where water moves backwards and then again forwards and you are double billed. 250,000 gallons of water seems unthinkable from that kind of fluctuations though.

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    flowing backwards should be prevented by a check valve though Sep 7, 2022 at 13:14
  • As others have stated, it would be impossible to have that high of a reading in 8 days with all the faucets turned on, let alone generate that much back and forth through fluctuations.
    – rtaft
    Sep 9, 2022 at 12:30
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Have you actually read your meter to see what the current usage is? That would be the first step in deciphering the problem. Does the meter show the same reading (or very close since you aren't actively using it) as the last invoice? A very simple explanation is that the meter reader accidentally added a leading digit to the reading. If that's the case, you can just call the utility company and they can fix it.

Our invoice shows both the current month and a small graph with usage for every month, along with the previous year. If yours doesn't, ask the utility for a statement that shows usage for the last year. This might show the typical usage and you can compare your current actual usage. This won't explain 250k gallons, but you can check the stream of usage (pun intended) to make sure they have been charging you over time.

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  • Also possible that they assume non-zero usage; if usage was 0, that could translate to the wrap-around reading for the meter. Sep 10, 2022 at 0:36

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