What could've caused this increase in water usage?

Their rate may have gone up, you could have a leak somewhere in your lines.

I’m not sure if water companies do this, but I know power companies do, they may have estimated your usage either this month or in the previous months. To save time on sending people out to check meters, power companies will “estimate” how much power you used based on how much you’ve used previously, how much other people with your size apartment/house use (or previous residents at your house have used). Later when they send someone out to actually check the meter, they adjust their estimate and either credit you the overcharge, or charge you more to make up for it. IF water companies do this, it could explain your differences.

@tedd Their rates didn’t change, so that’s not it. Plus, as I stated, they’re saying we used 5000 more gallons this month than last month. That wasn’t a guess on my part. Also, this house is brand new, so I’m not sure how likely a leak would be.

@livelaughlove21 Not sure where the leak would be either, but don’t let it being new make you think that’s an impossibility. New things break too :).

Could it be an estimated amount? Again I’m not sure if water companies do that, but it would explain it.

Go back to quick showers for a month and see what your bill looks like. How big is your bathtub?

In general, a fast shower will use much less water than that needed to fill an old-fashioned tub.

I have a low-flow shower head and can also turn it off easily while soaping and lathering, then turn it back on for a quick rinse.

Low-flow shower heads It might make sense to install one of these as a way of saving a little water.

A leak may not be likely but put some food coloring in the toilet tanks and let them sit overnight. Any color in the bowl means it is leaking. There maybe a timing issue, or a partial month in the billing cycle. The sprinkler system could have a bad solenoid and be leaking, also there maybe a loose connection in the plumbing leading to the sprinklers. If you have access to the water meter look at it and see if it moving when there is not water usage. A new house should have a warranty for the first year.

It does sound like it could be an estimate, like @tedd suggested. A quick call to your water company might solve the mystery.

Call the water company and have them come out and do an assessment. a new house COULD have a leak. Maybe the meter is broken, maybe they changed out the meter while you were at work. Maybe the meter reader transposed a number. Just call and they will help you investigate.
by the way, baths DO use more water than showers. Mine holds 50 gallons. an efficient shower head and you probably don’t use 10 in the shower.

Could be a leak. Does the bill divide up the water and sewer? Is it the water only that increased? If the water was 30 and the sewer 25 and now the water is 55 and the sewer 25, your water increase is almost double. The leak could be in your irrigation outside. An animal could have cut through a line, or someone may have driven over a sprinkler head.

If you take long showers the bath is not much more water if any, but if you take quick showers the difference can be more than you think between your shower and your bath.

Just a thought, has your water heating bill gone up? (Gas or electric, depending on how you heat your water.)

@Judi Nope, it stayed the same.

If I had someone come out to check the meter (the water company?) or to see if there’s a leak (plumber?), would the service call be covered under the warranty, most likely, or would it just be a repair that’s covered?

The water company would probably do it for free. They have programs to encourage water conservation. If they find a problem you could go back to the builder for repairs.

On average two people will use about 100 gallons per day if they are not careful. Conservative people will use half that. Is it possible your first bill was underestimated. so they were making up for it on this bill?
You would hear a 5000 gallon per month leak Turn off everything and stand near the meter head. Put your ear right up to it. It should be silent. Now have someone else open a faucet. You will hear the change.

Another way to gauge whether it’s the bath/shower change is (assuming you shower in the same tub you bathe in) to plug the drain and see just how full your tub gets during a typical shower; if it only fills partially, then the baths are the culprit.

My initial thought was that the first month was an estimate, as others have suggested. Also, the first month may not have included the full billing cycle (compare the time period on the bill relative to when you moved in). Also, have you been watering new landscaping or houseplants that maybe you didn’t have right from the first day? Car washes? etc?

You also should always compare to your neighbors bills.

To save water, we do laundry only one day a week (unless necessary).
You can put a brick or two in your toilet tanks, which reduces water usage.

That’s all I got.

Leak?

I can program my dishwasher to run at off-peak hours (1:00 AM to 6 AM).

Have you considered showering together?
Half the water usage and twice the fun.

Make sure everything is off in the house (including hose bibs outside). Then go to the meter (usually in the ground close to the road). Lift up the cover, (you may have to clear some dirt off of the meter gauge), and see if there is any visible movement. If not, then make a note of where the gauge is and check again say 2–4-6–8 hrs later (as long as you possibly can wait, without using any water). If the gauge has moved = leak. If not = no leak, so take fewer showers/baths. I take one once a week! wether I need it or not!! ;)

Make sure all your commodes are not leaking or running continuously.
A friend of mine had a toilet that was running all the time and it wasn’t a bathroom she ever used, so when her bill doubled in one month, she found the reason.