First thanks for taking a look at my question.

Okay looking at my water usage online reveals that between 4am-5am water is being used. The water usage ranges between 1 gallon to 10 gallons. I live alone & I am asleep at this time. I know I'm not sleepwalking & using water at this time.

I've check the toilets for leaks with dye tablets. Also checked that it wasn't overflowing. Have checked for leaks in the water heater. Did not find any leaks on these.

I have placed bowls under the sinks to see if there was anything leaking at night. Nothing there. So then I tried turning off the main water shutoff valve to the house. Interestingly enough the water leak at this time stopped for all 3 days I did this.

Now I've started to shutoff individual water valves. After trial & error each day I seemed to have found the culprit. Turning off the water to the washing machine seems to have stopped this leak for the 2 days I tried it. Now I'm trying to determine if it's the hot or cold water to the machine that is leaking.

However, this is really perplexing. First the machine is not on during this time so how could it be using water? I've checked the machine to see if water was there & no water. Heck, I've even unplugged the machine while still leaving the water valve on to it & water was used! Checked the machine & no water inside of it? I figured if somehow the machine was pulling water then by turning it off it shouldn't be able to drain it. How can water be used when the machine is not even turned on & specifically between 4-5am?

Suggestion, close the stop valve on the cold water input to your water heater before going to bed each night for a week and see what happens.

Thanks for the tip. I will try this soon & post results.

Are you thinking the water heater has a leak in the pipe coming into to it? 99% of the time I get the water usage between 4-5am. I don't normally start using water until 7am. Once in a while though, the water usage will be between 6-7am or no water usage at all. But those are the 1% oddities.

No, I'm thinking that the water heater comes on, water expands, pressure increases, water has no where to go but back up the cold water pipe. If you do not have a check valve and the meter does not have a check valve it goes back through the meter. When water in heater cools, pressure is reduced and water flows back through meter into the tank.

Never heard of being able to monitor water usage by time of day.

Do you have a pressure regulating valve, do you know what your water pressure is?

Hmm. Getting double charge for the same water! Haha.

Well I have some updates to report. First, I'm not sure what you mean by a "check valve". The water heater has a "temperature & pressure relief valve". So I assume if extra pressure needed to be released it would do so through this extra pipe. It's also a gas water heater.

Next, I'm sad to report that after 3 days I again started noticing water usage around 5am. This was with the hot water to the washing machine turned off. Thursday 2 gallons were used & Friday 4.3 gallons were used. So now I'm going to turn off the cold water to the washer & see if any water is used & if not for how long.

After this I'll try your suggestion although I don't think it would apply if my heater has a relief valve.

Hmm. Getting double charge for the same water! haha.

Well I have some updates to report. First, I'm not sure what you mean by a "check valve". The water heater has a "temperature & pressure relief valve". So I assume if extra pressure needed to be released it would do so through this extra pipe. It's also a gas water heater.

Next, I'm sad to report that after 3 days I again started noticing water usage around 5am. This was with the hot water to the washing machine turned off. Thursday 2 gallons were used & Friday 4.3 gallons were used. So now I'm going to turn off the cold water to the washer & see if any water is used & if not for how long.

After this I'll try your suggestion although I don't think it would apply if my heater has a relief valve.

Not the same. In older water systems water could backflow into the water supply. In a pressurized system, water flows to the lower pressure. If your water pressure becomes greater than the supply, water will flow back. That is the purpose of a check valve, to prevent this from happening. The PRV only goes off at pressures above the set point which is most likely above the water supply pressure. In another example, let's say your house pressure is 60 # and the city supply is 80#. Now, at 5AM, a big water User turns on flow and momentarily pressure drops to #50. You can get flow from your system to the city and when it pressurizes up, water flows in. Not saying this is the answer but a possibility. I would do this. Shut off the water at the street before you go to bed and see what happens when you.open it back up. If you get water flow, you have a leak somewhere. Almost every new house built today uses a check valve and expansion tank and a PRV is mandatory on HW heaters.

Brian's got the idea but I think he mixed up his PRV and T&P terms.
A check valve is an automatic valve that lets water flow only in one direction.

My thoughts are that as the water heater comes on and pressure builds, the water in your house pipes and the pipe to the street builds. Water then flows through the meter back to the city pipe. Then as the water in the heater cools and pressure drops, water flows back through the meter to your house. This probably goes on all the time but you just don't know it.

Some PRV's (pressure reducing valves) have an check valve built into them some do not. The T&P valve is a safety device and the pressure setting is much higher than we are talking about.

By closing the valve on the cold water input line to the water heater, you prevent the pressure in the water heater from moving back up the line to the street. This is just a way of verifying the hypothesis. If the hypothesis prove correct you would then install check valve either on the cold water line to the water heater or on the main line to the house. Water could be passing from the hot to cold in the mixing valve of the washing machine if the pressures are uneven. So close the cold water input valve to the water heater and one of the valves on the washer, doesn't matter which, and monitor.

@ hkstroud - sorry I just noticed I missed a few of your questions. In the city I live in there we have the option to go online & see our water usage. This system is called aquastar. Attached is a screenshot of what it looks like.

The house is 19 years old. I don't know if it has a pressure regulating system but I'm assuming that I don't. No, I do not know the water pressure in my house.

Ok I will forget about turning off the water to the washing machine. Instead I will go with turning off the cold water to the water heater for 1 whole week. This might seem like an obvious answer but there are 2 pipes going to the water heater. Only 1 of them has a round water knob, so I'm going to assume this is the cold water & this will shut it off since the other pipe has no handle. Also, if I shut off the cold water to the heater then if water pressure is building up then where will it be released to?

@ ma0641 - thanks for the explanation of water pressure.

Yes, the pipe with the valve is the cold water input. The pressure will not be released. It will be well with in the limits of the water heater, so not to worry. If pressure were to exceed the limits of the water heater it would be released through T&P valve. Note, also close one of the valves at the washer just to make sure the pressure difference does not cause water to pass through mixing valve.

Of course the water heater may have nothing to do with this. As Brian pointed out, if a heavy user starts up that time of the morning there could be a drastic drop in city pressure and that could be causing the back flow. We are just trying to find the cause right now.

With that little usage you must be in the AZ desert.

Ok got it but does it matter what valve inside the house I close? Since water was still used with the water to the washer turned off, then I could turn off the valve to a sink maybe instead of the washer?

I actually live in the Raleigh, NC area. I live by myself & I try not to use too much water. So it just kills me when I see water being used that is not being used by me! Not to mention that my water bill would be lower than what it is.

PRV TPV XYZ Yikes!? TPV does not enter into this issue, that's on the HW heater. Shutting off the CW to the heater does nothing to the HW Pressure, it is hot now and won't get hotter. The big issue is house vs system pressure. If you are on city water you have a main regulating valve, usually right where the water pipe enters the house. Look for a brass inverted conical device, probably with a metal tag. In looking at your water usage, I think this is needless worry.
You are probably charged a minimum, mine is 2000 gallons per month, and at the usage I see you aren't close. Check your minimum.

If you close the cold water valve on the water heater you will eliminate (or confirm) the water heater from being the possible cause of the back flow. If you close the main valve to the house you will prevent water from flowing (in either direction) but you won't know what was causing it.

One more update. It seems I can't pinpoint this leak. In past I had shut off the main water valve to the house from inside the house. I did this for 3 days & no water usage. So that let me to believe it was something inside the house. Turning the water (hot & cold) off to washer for 3 days showed me that no water was used. Then I tried opening 1 valve to the washer & seeing if usage happened. It did. Then I tried with the other valve & usage again. So that wasn't the culprit.

Just this Monday night I turned off the water to the house again. Sure enough my suspicions came true. I had water usage! So now I know it's not inside my house. It's either the main service line going into the house from the street that has a leak (although a 5am leak & not an all the time leak just boggles my mind) or just something wrong with the meter the water company uses (which they are really a pain to deal with - they want me to check the main service line which would cost a lot of money to dig up & check before they send a service tech to check the meter... arrrgghhh).

So now my last hope is to turn off the meter at the street before bed, which sucks, & according to the city is considered "tampering", lol & then turn it back on in the morning, which also sucks. If I get water usage when I do this it has to point to a problem on their end right? When I asked them this they said "possibly".

They also asked if I used a humidifier at home, irrigation system or heat pump. I don't have an irrigation system (I let nature water the lawn). I'm sure I don't have a humidifier, which I thought you buy at a store & plug in to a wall outlet? As far as a heat pump I don't know what was meant by that. Were they talking about my air conditioner? If so my heat is gas & cold is electric.

@ ma0641 - you said the following:

"Shut off the water at the street before you go to bed and see what happens when you.open it back up. If you get water flow, you have a leak somewhere."

I may be misunderstanding your statement but wouldn't I expect to see water flow when I open it back up?

@ ma0641 - you said the following:

"Shut off the water at the street before you go to bed and see what happens when you.open it back up. If you get water flow, you have a leak somewhere."

I may be misunderstanding your statement but wouldn't I expect to see water flow when I open it back up?

No. If there is no usage, the water should still be at the same pressure when you shut it off as long as you don't flush a toilet or open a tap. Water doesn't compress so it should occupy the same volume, assuming no leaks.