What are common reasons for an unusually high water bill?

Do the meter test first, because it answers the biggest question. EPA says to check your water meter before and after a two-hour period when no water is being used. If the meter changes at all, you probably have a leak. Turn off the dishwasher, the washing machine, the ice maker and the irrigation system, and make sure nobody flushes a toilet. Then read the meter, wait two hours and read it again. Our water meter leak test page shows what to look for on the dial.

If the meter did not move, the water is being used on purpose. Look at what changed in your household. If the meter did move, keep reading, because a leak is very likely.

Your bill can help. A Phoenix bill shows a 13-month history of monthly usage in gallons, according to the City of Phoenix. A sharp jump in one month points to something that started recently, like a new leak or a change in use. A steady climb over several months points to something that has been getting worse, such as a slow leak or an aging fixture.

Most household leaks are simple ones, and EPA says they are often easy to fix. It also says the average household's leaks can waste more than 9,300 gallons of water a year, and that nine percent of homes have leaks that waste 50 gallons or more per day.

• Toilets. The most common single cause. EPA says an old or worn flapper can cause a toilet to flush on its own or silently leak thousands of gallons a year. Test with a few drops of food coloring in the tank. If color shows in the bowl after 10 minutes, the flapper is leaking. See how to fix a running toilet and how to replace a toilet flapper.
• Faucets. EPA says a faucet that drips once per second can waste more than 3,000 gallons a year. See how to fix a dripping faucet.
• Showerheads. EPA says a showerhead leaking 10 drips a minute wastes more than 500 gallons a year.
• Hose connections and hose bibs. EPA says to check garden hoses where they meet the spigot. See outdoor faucet hose bib leaking.
• Irrigation systems. EPA says a leak 1/32 of an inch wide, about the thickness of a dime, can waste about 6,300 gallons of water a month. EPA also says a household with an irrigation system that is not properly maintained and operated can waste up to 25,000 gallons of water a year. See how to fix drip irrigation.

Then it may be hidden. A leak in a wall, in the yard supply line or under the slab does not show on the surface at first. The signs are a meter that moves when everything is off, a warm spot on the floor, the sound of running water when nothing is on, or a wet patch in the yard with no rain. Our pages on high water bill with no visible leak, signs of a slab leak in Arizona and pinhole leaks in copper pipes cover the main suspects, and how plumbers find hidden leaks explains the tools used.

If you have a pool, the same principle applies to its plumbing. Water that disappears from a pool is water you pay to replace. See how to find a pool plumbing leak.

Not every high bill is a leak. Some are simply more use, and they are worth ruling out:

• Summer watering. EPA says outdoor use is more than 30 percent of household water use on average and can reach 60 percent in arid regions. A hot month with longer irrigation cycles can raise a bill sharply.
• Guests or a bigger household. More people means more showers, laundry and flushing.
• New landscaping. New plants and sod need extra water while they establish.
• A new appliance or habit. A new pool, a water feature or a new routine with a hose can move the numbers.
• A longer billing period. Look at the dates on the bill. A period with more days means more use on the same bill.
• The base fee thresholds. Phoenix says the water base fee includes 5 units (3,740 gallons) from October through May and 8 units (5,984 gallons) from June through September, with 748 gallons equal to one unit. That means the same use can look different on the bill in different seasons.

A simple way to sort real use from waste is to compare the same month across two years. Your usage history shows 13 months, which is enough to line up this month against the same month last year. If the two match, the bill is probably a matter of season. If this month is far above last year's and nothing at home changed, the extra water went somewhere it should not have. Write the difference in gallons, then in units of 748 gallons, so you can talk about it with the utility in the same terms its bill uses.

If a bill has doubled, ask which of the above changed. A sudden doubling with no change at home is a strong clue for a leak. EPA suggests checking your usage during a colder month such as January or February, and says that if a family of four uses more than 12,000 gallons per month then, there could be serious leaks.

Do not wait for the next bill to find out. A leak wastes water every hour it runs, and the bill is only the record of it. A toilet leak that costs you a little each day is easy to ignore, and it is also the easiest one to end.

Work in this order and stop when you find the cause:

1. 1Read the bill's meter numbers and confirm the reading matches your meter.
2. 2Do the two-hour meter test with everything off.
3. 3Test each toilet with dye.
4. 4Look at every faucet, showerhead, hose and irrigation zone.
5. 5If the meter still moves and you cannot find a leak, call a plumber to locate it.

Fix what you find, then watch the next bill. Write down the meter reading before and after the repair so you can prove the change. If the high bill has already arrived, read what help exists for a high water bill in Arizona, and if you want lower bills in general, see the best ways to reduce a water bill in Phoenix.

The City of Phoenix says the average household loses more than 10,000 gallons of water each year through leaks, so finding one is common and fixable. HQ Plumbing & Air is licensed and insured, gives free estimates and upfront pricing, and answers 24/7.