If your water bill suddenly jumped and nobody is using more water, the most likely cause is a toilet that runs without anyone noticing, followed by a dripping faucet or fixture, a water heater relief valve discharging, an irrigation system, or a leak in the underground line between the meter and the house. You can usually find out which in under an hour with the water meter and a few drops of food coloring. Start with the meter test below. It tells you whether water is leaving the system when everything is turned off, and it points you toward where to look next.

This guide walks through each check in the order that finds the most leaks fastest, then covers what to do once you know, and how leak responsibility usually works in a rental.

Step one, confirm it is a leak and not a billing issue

Before you hunt, compare the bill against the same months last year and look at the usage in gallons or units, not just the dollar amount. Rate changes, a longer billing period, an estimated reading, or a read that caught up after a missed month can all make a bill jump without any change in use. If usage really did go up and nothing in the household changed, keep going.

Step two, the meter test

Your water meter is usually in a box near the street or sidewalk with a lid you can lift. Inside, most residential meters have a small triangle, star, or spinning dial called the leak indicator, along with the main register.

  1. Turn off every faucet, shower, and appliance that uses water. Make sure the dishwasher, washing machine, ice maker, and irrigation system are not running.
  2. Look at the leak indicator. If it is turning with everything off, water is moving somewhere.
  3. For a slower leak, write down the reading on the register, wait an hour or two without using any water, and read it again. Any change means a leak.

Next, find your home's main shutoff valve, often in the crawlspace, the garage, near the water heater, or where the line enters the house. Close it and check the meter again.

  • Meter stops when the house valve is closed. The leak is inside the house. Go to step three.
  • Meter keeps moving with the house valve closed. The leak is on the service line between the meter and the house, or on an irrigation line that branches off before the house valve. Go to step five.

Step three, check the toilets first

Toilets are the most common source of silent leaks. A worn flapper lets water seep from the tank into the bowl, the fill valve tops the tank back up, and the cycle repeats all day and night. You may hear the tank refill on its own every so often, or you may hear nothing at all. The EPA's WaterSense program estimates that a leaking toilet can waste as much as 200 gallons a day.

The dye test:

  1. Take the lid off the tank.
  2. Add a few drops of food coloring or a dye tablet to the tank water.
  3. Do not flush. Wait fifteen to thirty minutes.
  4. If color shows up in the bowl, the flapper or flush valve is leaking.

Also look at the overflow tube in the tank. If water is running into the top of the tube, the fill valve is set too high or failing. Do this for every toilet in the house, including the one in the basement or bonus room nobody uses, because that is often the one that has been running for months.

Step four, check everything else inside

  • Faucets and showerheads. A steady drip adds up over a billing cycle. Check tub spouts too, since a worn shower valve cartridge can let water trickle into the tub.
  • Water heater. Look at the temperature and pressure relief valve and its discharge pipe. If the pipe is wet or dripping, the valve may be failing, or the system pressure or temperature may be too high. That is a safety device, so do not cap it. Also check the tank base and fittings. Our article on water heater age and failure signs covers what a leaking tank usually means.
  • Appliance connections. Washing machine hoses, dishwasher supply lines, and refrigerator ice maker lines.
  • Under sinks. Supply lines and shutoff valves, especially older ones.
  • The crawlspace. Many Middle Tennessee homes sit on a crawlspace, and a leak on a supply line under the floor can run for weeks before anyone notices. Look with a flashlight for standing water, wet soil, dripping pipes, or wet insulation. If you see water, follow the pipe back to the source.
  • Floors and ceilings. Soft spots, warped flooring, stains below a bathroom, or a musty smell can point to a hidden supply or drain leak.

If the meter test showed a leak inside the house and none of these turned it up, the leak may be inside a wall or under a slab. That is the point to call a plumber with leak detection equipment rather than open walls on a guess.

Step five, leaks outside the house

If the meter keeps moving with the house valve closed, the water is escaping between the meter and the house.

  • Irrigation. If there is a sprinkler system, shut it off at its own valve and check the meter again. Broken heads, cracked lines, and stuck valves are common, especially after the first hard freeze.
  • Outdoor spigots. Check every hose bib for drips, and look for a split pipe inside the wall behind a spigot that froze last winter.
  • The service line. Look along the path from the meter to the house for a wet spot, a patch of grass that is greener than the rest, a sunken area, or water in the meter box itself.

In most places, the water utility is responsible for the line up to and including the meter, and the property owner is responsible for the line from the meter to the house. Call your utility to confirm where that line falls for your property before anyone starts digging. Some utilities also offer a one time adjustment on a leak inflated bill once the repair is documented, so keep the invoice and photos and ask.

What a high water bill means in a rental

In a rental, a leak is a repair, and who pays the water bill and who pays for the fix are usually two separate questions. Most leases put water on the tenant when it is billed in their name, but the repair of a failing flapper, a leaking supply line, or a broken service line is generally the landlord's responsibility under Tennessee law because it is part of keeping the plumbing in working order. A tenant who caused damage is a different case. Our article on landlord versus tenant repair responsibility in Tennessee covers where those lines usually fall.

For property managers, a sudden spike on a tenant's bill is often the first sign of a problem in the unit. A quick dye test at every turnover and every routine visit catches flappers before they turn into a complaint.

Small fixes and when to call

A flapper or fill valve replacement is one of the easiest plumbing repairs there is, and many homeowners do it themselves with a part from the hardware store. Call a plumber when:

  • The meter test shows a leak and you cannot find it.
  • The leak is in the service line, a wall, a ceiling, or under the floor.
  • The water heater relief valve is discharging.
  • There is water damage that needs to be dried and repaired once the leak is stopped.

How we help

Our plumbing work covers leak tracing, toilet and fixture repairs, supply line replacements, water heaters, and the drywall and flooring repairs that follow a leak. Submit a work order with the address and what you are seeing. We confirm within two business hours and schedule routine work within 48 hours, with a flat quote before anything starts.