Mysterious water usage

I've been having a weird water usage spike at night. I've narrowed it down to a mystery usage of water in the middle of the night, ranging anywhere from 60-100 gallons. The house has 3 bathrooms and it's just me and my wife in the house. Whatever it is, it is not a constant leak because I never see the flow indicator moving when I make my readings. Due to various tests I've run, I've ruled out the irrigation (landscaper said it was working fine), water softener, the toilets, and really anything inside the house. I'm definitely a plumbing novice, so I have no problem calling a plumber, but I just want to make sure it's not something obvious first. I'm tired of doing constant meter readings, so I'm hoping you guys have a suggestion. If interested, I've included some more facts below. Thanks for your help.

Relevant facts:

-Usually this spike seems to be happening around 1-2am. I say this because sometimes I go out and make a reading before I go to bed around 1:30am, and sometimes the spike has already occurred. On these nights, I'll still make a reading in the morning and I see no excess usage.
-Water company said it might be ghost flushing, so I've shut off water to the upstairs toilets over night, and the spike has still occurred. Plus, I don't see how it could be a toilet if the water is being used early in the night then stops on its own?
-I went away for two weeks in September, at which point I shut off one of the shut off valves in the garage. After returning and making readings, and accounting for the water my irrigation used, I was still using about 75 gallons a day of water. (full disclosure: for some reason, I have 3 shut off valves in the garage and another one connected to the water heater - I was told that any of the 3 would shut off water to the house?)
-After examining the shut off valves, I noticed that the one I shut off may not have shut off the water softener. The water softener is set for 2am, and we have not heard it go off every night, so I always doubted it was the cause. To be sure, I turned the by pass valve on one night and a spike still occurred. The spike was on the low side (about 60 gallons).
-Only things I can think of that use water in this house are toilets, showers, sinks, ice maker, reverse osmosis system, water softener, water heater, dishwasher, washing machine, and irrigation. Assuming the shut off valve I used was working properly, then it shouldn't be anything inside the house.
-The water company came out and tested the meter, and they say it's working properly.
-This may not be relevant, but for the last couple of months, I get a faint sulfur/rotten egg smell from the master bedroom sink. It's not constant and only seems to be there when the sink hasn't run for a while. I also heard some squeaking pipes in the master as well, and again, only when the faucet hasn't been used in a while.
-I'm desperate, so my next move is to turn off all 4 shutoff valves in the garage over night, just to make sure my previous tests were accurate. After that, I'm going to turn the water off at the main, just to be sure it really isn't the meter.

 

Welcome to the forums!

Have you checked your water pressure with a gauge? City water pressure typically spikes at night. There could be a leak that doesn't really appear until the water pressure rises.

 

That's a fairly common problem and happens as the water in the trap evaporates from non use. A few seconds of running the water should take care of that.

It could also be a leak in the vent line that goes thru to the roof. That usually passes thru an upstairs bathroom.

You're talking about major water use. I think I'd try shutting the water off to the sprinkler system as a test.

 

Lines ran through a slab?
Added red food coloring to the toilet tank at night to see if it ends up in the bowl?
What time is the timer set for to backwash the softener?

 

Thanks for the replies.

When you say a leak in the vent line, you mean that's causing the rotten egg smell, or the mystery water usage?

The sprinkler system only runs every other day in September, and the spike is still happening every day. Should I still try turning the sprinklers off? Outside of pressing off on the irrigation clock, how would I do this?

I have not checked my water pressure with a gauge. That's an interesting theory about the leak happening when the pressure increases. Could that be enough to explain 60-100 gallons? How would I go about testing this?

Thanks again.

 

Sorry, not sure what you mean by lines run through a slab?

I have not tried the food coloring trick as I just directly shut the water off at the toilet over night, and the spike still occurred. Plus I had it shut off for the two weeks. Could it still be the toilets?

Water softener is set for 2AM, and the current time on the softener is set right.

Thanks.

 

Spike happens at 2 AM, softener set for about the same time, Hmm.
Is your house on a slab? If the water lines where ran through the slab and there copper lines you can plan on them leaking at some point and having to reroute them at some point through the walls or attic with PEX.

 

I didn't think it was the water softener because I had the bypass on one night and the spike still happened. It's possible that the bypass is faulty as the softener is older. I'm going to try all the shutoff valves tonight and see what happens.

Not sure if it's on a slab or not.

 

On a slab would mean you have no basement and that the water lines are running thru concrete.
Usually with a slab leak..... it always leaks.... it wouldn't just happen at night unless the water pressure skyrocketed and forced its way thru.

There should be a large line near the meter going outside to the sprinkler system. Usually you'll see a check valve system for the sprinkler on the side of the house. There should be a valve between the city supply and that check valve.

 

Usually a house has a pressure reducer valve shortly after the water supply enters the house. It prevents the water pressure from rising above a certain point - unless the PVR has become defective. The water line from the meter [assuming it's at the street] is not protected by the PVR and that pressure is very prone to hikes during low demand hours. I live on top of a hill [small mountain] and have low water pressure [often only 20-30 psi] but it will double during the night time hours.

 

The water softener will still recharge even if it's on bypass. 60-100 gallons is a LOT of water for a recharge. I'd try unplugging your softener for a few days and see if the usage goes away. Most (all?) softeners should keep their settings even when unplugged, though you may need to reset the clock when you plug it back in.

Same with the irrigation. I'd turn off the water for the irrigation to confirm you don't have a leak or valves inadvertently turning on.

In my mind, it's got to be one or the other. A toilet or pipe leak would be much more consistent.

 

Mystery solved. It turns out my irrigation clock has two separate programs. A second program was running in the background, so the sprinklers were running too often. Unfortunately the times on the second program were close to the first program, so they always blend together when I do one of my meter readings. And my landscaper never mentioned it when he came out to look at it, so I always ruled them out.

Long story short, I lived up to my screen name. I apologize if I wasted anyone's time. On the plus side, I learned how to replace a flush valve and I know how much water each of my appliances use, so there's that. Thanks for the help fellas.

 

Glad you got it figured out and now you're a little brighter to boot