In one commercial insurer's breakdown, roof leaks and toilets each account for about 15% of water damage claims, followed by sprinklers, water heaters, air conditioning, vacant buildings, boilers and sewer backups. Plumbing supply failures, from corroded pipe to failed fittings and hoses, sit behind most of the interior losses.
What does the claims data say?
Chubb, which insures commercial property, ranked the top sources of interior water damage loss in commercial buildings and gave each a share of claims or losses. Its shares come from a Chubb publication on water damage trends, and they describe Chubb's book of business, not every building in Arizona. Still, the order is useful.
| Rank | Source | Chubb's share |
|---|---|---|
| 1 | Roofs | an estimated 15% of claims |
| 2 | Toilets | 15% of losses |
| 3 | Sprinklers | 14% of loss |
| 4 | Water heaters | typically 11% |
| 5 | HVAC | about 8% |
| 6 | Vacancy | about 8% |
| 7 | Boilers and machinery | 7% |
| 8 | Sewer and sewage backup | 5% of claims |
| 9 | Water tanks | 4% |
| 10 | Water mains | 3% |
Read it by trade. The roof is a roofing problem. Sprinkler and HVAC losses belong to the fire protection and mechanical trades. The rest, toilets, water heaters, supply lines, vacancy leaks, sewer backups and mains, are plumbing, and together they make up a large share of the table.
Chubb's other risk-engineering article lists the key factors in large loss events, among them "Leaky, defective or corroded roofs, domestic water service or drainage plumbing and fittings," along with "The use of lesser quality materials and/or incorrect installation," "Inadequate maintenance and inspections," and "The absence of, or incorrect use of, water leak detection and shut-off systems."
Why do toilets and water heaters cause so much damage?
They are everywhere, they run on pressure, and nobody looks behind them. On toilets, Chubb says "Especially in multistory buildings with stacked plumbing, toilets are a major cause of interior water damage." A failed supply hose or a fill valve that never shuts off puts water on a floor that drains to the ceiling below. Chubb's tip is to "replace all hoses every three to five years, even if they appear normal." Our page on commercial flushometer toilets that keep running covers the valve side.
Water heaters fail by age. Chubb says water heaters have a high failure rate after 7 to 10 years and should be replaced before they contribute to losses, with a drip pan under the heater and an automatic shutoff valve near it. Our guide on how often a commercial water heater should be flushed and serviced is the maintenance half of that advice.
Why do small leaks turn into big losses?
Because water has time. Chubb's case studies describe a corroded pipe that burst and destroyed equipment in a lab, a failed relief valve coupling in a high-rise that sent water from the 16th floor to the basement, and a failed reducer fitting on an 18th-floor riser that spread damage to 65 units. In each, the failure was a pipe, a fitting or a coupling, and the damage came from how long and how far the water ran.
Chubb also points out that even a small crack is not small: according to its article, a crack in a one-eighth-inch pipe can leak 250 gallons of water per day. Interior corrosion, it adds, "can be the underlying cause of pipe defects that make them more susceptible to bursts," which is why corrosion is hard to see until it fails. Pipe age and material matter here. See our page on pinhole leaks in copper pipes for how that starts.
Vacant buildings are the worst case of "nobody noticed." Chubb says vacancy emergencies account for about 8% of commercial water damage losses because "If a building is empty, it's less likely that water damage risks will be detected early." Its advice: shut off water where it's not needed. If you have a vacant suite, closing the water to it is a simple first step.
What does a sewer backup add?
A different kind of water. Chubb puts sewer and sewage backup at 5% of claims and calls them "especially messy and undesirable." It says they are "often triggered by events such as excessive rain" and can be reduced by "monitoring, and clearing clog-prone areas such as wastewater lines and drainage systems." The same insurer notes that backups need their own protection, such as drain check valves, because a supply shutoff doesn't touch them. Our page on commercial insurance for a water leak versus a sewer backup explains why the two are often treated differently.
What can an owner do about it?
Start with the legal baseline. The 2024 International Plumbing Code puts the maintenance duty on the owner: "The owner or the owner's authorized agent shall be responsible for maintenance of plumbing systems." Phoenix adopted the 2024 IPC with local amendments, and its amendment list does not change Section 102.3.
A practical walk-through, matched to the claims table:
- 1Know your shutoffs. Label the main and each zone or suite valve, and test them. Planning a commercial water shutoff shows how.
- 2Replace supply hoses on a schedule. Toilets, sinks, ice machines, coffee brewers and dishwashers all have them.
- 3Track water heater age. Put the install date on a tag and plan replacement before failure.
- 4Check vacant suites. Walk them on a schedule, and close the water to them.
- 5Keep drains moving. Clear clog-prone lines before a storm season, and know where your cleanouts are.
- 6Consider leak detection. Sensors and automatic valves can catch what a walk-through misses. See whether automatic shutoff systems are worth it.
When something does fail, the order of operations matters, and who handles a commercial leak after the plumber stops the water covers it.
HQ Plumbing & Air replaces water heaters, repairs and replaces supply piping, and cleans drain lines for commercial buildings. We're licensed and insured, with 24/7 emergency service, upfront pricing and free estimates.