Start at the building's master meter during a quiet overnight window. If it keeps moving, water is running somewhere. Then narrow it by riser, building or unit meter, and check each unit's toilets, faucets and showerheads. Arizona's landlord-tenant act requires two days' notice to enter a unit unless it is an emergency.
Is it a leak, or just more use?
Check the meter at a time when almost no one is using water. Pick the middle of the night, ask the crew to shut off irrigation and any cooling or laundry equipment on a timer, and read the master meter's low-flow indicator, or write down the register twice, fifteen minutes apart. If the meter is moving, water is running through the building at a time when it should not be. Our page on investigating overnight water use in a commercial building walks through the closed-building method, and the water meter leak test covers the reading itself.
Scale tells you how much to worry. EPA's multi-unit housing slides give the arithmetic: "One gallon per minute is equal to 1,440 gallons per day." A steady trickle you cannot see at any one fixture can still add up to the whole difference in a bill. A running toilet or a single bad diverter is a typical cause, and many buildings have more than one.
If the meter stops at night, the extra water is being used rather than wasted. Look at what changed: new residents, a vacant unit that was filled, irrigation settings, a pool top-off, or a laundry room. Our page on comparing commercial water bills shows how to line up billing periods before drawing conclusions.
How do you narrow it to a building, riser or unit?
Divide the property. Each cut halves the search.
- Multiple meters. If the property has more than one master meter, read each one overnight and find the one that keeps moving.
- Submeters. If units or buildings have submeters, read them at the same time. A unit meter that keeps spinning at 3 a.m. points straight at that apartment. Using submeters to narrow a leak explains the comparison and its limits.
- Isolation valves. Where building or riser valves exist, a plumber can close one section at a time while a person watches the meter. If the meter slows when a riser closes, the leak is on that riser. Warn residents before closing anything, and do not close valves you cannot identify.
- Common areas. Irrigation clocks, pool or fountain fill valves, laundry rooms, car wash bays, and the water heater room sit on the same meter. Check them before entering units.
If the water is leaking underground between the meter and the building, the meter moves with every valve inside the building closed. That is a buried line leak, and no amount of unit inspection will find it.
What do you check inside each unit?
Start with the toilets. EPA says "Old or worn-out toilet flappers (e.g., valve seal) can cause leaks," and that "An old or worn flapper can cause your toilet to flush on its own or silently leak thousands of gallons a year." Its Fix a Leak Week page also lists dye tabs among the sleuthing gear. Put a dye tablet or a few drops of food coloring in each tank, wait without flushing, and look for color in the bowl. See how to fix a running toilet for the flapper repair.
Then work through the rest of the unit:
- 1Every faucet and shower valve for drips.
- 2Showerheads and tub diverters. EPA's slides note that a leaking diverter wastes water only while the shower is on.
- 3The water heater's relief valve discharge pipe.
- 4Washing machine supply hoses and ice maker lines.
- 5Under-sink supplies and angle stops.
- 6Water softener or filter drains, if any.
Some of the smallest leaks are inside cabinets or walls. A bathroom exhaust vent that is damp, a stained ceiling in the unit below, and a floor that feels spongy all deserve a closer look.
How do you get into occupied units legally?
Arizona's Residential Landlord and Tenant Act sets the ground rules for apartments it covers. A.R.S. 33-1343(D) says "Except in case of emergency or if it is impracticable to do so, the landlord shall give the tenant at least two days' notice of the landlord's intent to enter and enter only at reasonable times." Subsection C says "The landlord may enter the dwelling unit without consent of the tenant in case of emergency." And if a resident has already sent a maintenance request, subsection B treats that notice as permission to enter for that purpose.
The same Act puts the plumbing on the landlord. A.R.S. 33-1324(A)(4) requires the landlord to "Maintain in good and safe working order and condition all electrical, plumbing, sanitary, heating, ventilating, air-conditioning and other facilities and appliances, including elevators, supplied or required to be supplied by him." So a sweep for leaks is part of owning the building. A written notice that tells residents the date, the time window, and that the visit is a water-use check keeps it routine.
Condominiums fall under a different law, and commercial buildings follow their leases. See who maintains lines in each setting for the lease side. How a landlord bills tenants for water is a separate topic, covered in Arizona submeter and RUBS billing.
When is it time to bring in a plumber?
When the meter test says water is moving and the toilet and fixture checks come up clean. At that point the leak is in a wall, a slab, a riser, or a buried line, and finding it takes tools. A plumber can isolate sections, listen to pipes, and use camera inspection or leak detection to mark the spot. Ask what area will be inspected and what methods will be used before you approve the work.
HQ repairs leaking fixtures, valves and lines in multifamily buildings, and gives an upfront price and a free estimate before work starts. This page explains general Arizona rules and is not legal advice.