The short answer: which interval is your tank on?
NFPA 25 (2020 edition), which Virginia enforces, sorts fire protection water storage tanks by what they are made of. NFPA 25-2020 calls for the interior of a steel tank without corrosion protection to be inspected every 3 years, and the interior of all other tanks to be inspected every 5 years. Size and age do not set the interval. Material and protection do.
The table below sorts common tank types onto those two intervals. Treat it as a planning guide, not a legal reading of the standard, and confirm each row with your AHJ against the edition it enforces.
| Tank | Interior interval | Category | Note |
|---|---|---|---|
| Steel tank without interior corrosion protection | Every 3 years | Steel, unprotected | The shorter interval. Bare steel in contact with water and air. |
| Steel tank with interior corrosion protection | Every 5 years | All other tanks | Ask your AHJ how it treats protection that has visibly failed. |
| Concrete tank | Every 5 years | All other tanks | Inspection looks for spalling, cracking, and deterioration. |
| Wood tank | Every 5 years | All other tanks | Inspection looks for rot and other deterioration. |
| Pressure tank or other construction | Set by material | Confirm with AHJ | The interval follows what the tank is made of. Confirm the category with your AHJ. |
Intervals: confirm the adopted edition with your AHJ.
Between interior inspections: the routine checks
The interior inspection is the big visit, but NFPA 25 also calls for more frequent checks that the owner or the owner’s staff usually handle. These generally include confirming the water level is where it should be, looking over the tank exterior, supports, and surrounding area for damage or anything that could harm the tank, and checking valves and gauges on the tank’s supply.
Cold weather adds another layer. Where a tank has a heating system, NFPA 25 calls for checking that it is working and that water temperature stays above the minimum during the heating season, and for low-water-level and low-temperature alarms, where installed, to be tested. Exact intervals for each of these checks vary by item and edition, so pull the routine schedule from the edition your AHJ enforces and keep it with your fire protection records.
Who is responsible
Under NFPA 25, the property owner or the owner’s designated representative is responsible for inspection, testing, and maintenance of the water-based fire protection system, including its water storage tank. A property manager often runs the schedule day to day, but the duty sits with the owner.
The AHJ, usually the local fire marshal, enforces the adopted edition and decides what it accepts. That includes whether an in-service interior inspection satisfies the interval for your tank. If you are unsure, ask the AHJ before the inspection is scheduled, not after.
Which edition applies: Virginia and the rest of FLOW’s area
Virginia gets to NFPA 25 through the Virginia Statewide Fire Prevention Code (SFPC). The 2021 SFPC took effect on January 18, 2024, incorporates the 2021 International Fire Code by reference, and through it references NFPA 25 (2020 edition). A later Virginia code cycle may move to a newer edition, so check with your local fire marshal before assuming which one applies.
FLOW serves Virginia, Washington DC, Maryland, North Carolina, and South Carolina. Each of those jurisdictions adopts its fire code on its own schedule and may enforce a different edition of NFPA 25 or add local amendments. That is why every interval on this page carries the same instruction: confirm the adopted edition and requirements with your AHJ.
What an interior inspection looks for
An interior inspection looks at the condition of the walls, floor, roof underside, and fittings that sit under the water. Inspectors generally look for pitting, corrosion, spalling, rot or other deterioration, debris and foreign material, aquatic growth, and sediment build-up, and they note the condition of the tank’s interior corrosion protection where there is any.
Sediment deserves special attention. It can hide the floor from view, and it is material the tank outlet can draw into the fire protection system during a fire. A good inspection records how much sediment is present and where, so the owner can plan next steps with the AHJ and other contractors.
How an in-service ROV inspection meets the interval
FLOW performs the interior inspection with the tank in service. A pilot lowers an underwater submersible drone (ROV) through a roof hatch and flies it through the full tank, recording video of the walls, floor, seams, fittings, and the tank outlet. The water supply stays in place for the fire protection system the whole time.
Because the tank stays full and in service, there is no gap in fire protection while the inspection runs, and the visit is usually shorter and simpler to coordinate with tenants and the fire marshal. After the visit, FLOW sends the owner the recorded video and a written findings report.
Whether an in-service ROV inspection satisfies the interval for your tank is the AHJ’s decision. Most owners confirm that with the fire marshal before booking. If a tank has to be taken out of service for other work, FLOW refers that work to a partner firm.
How the in-service method works, what the pilot records, and what the AHJ may accept: underwater submersible drone (ROV) tank inspection.
What the inspection report includes
Keep the report with the rest of your NFPA 25 records; the AHJ may ask to see it. A FLOW in-service ROV report generally includes the site and tank identification, the date of the inspection, the tank type and approximate size, the method used (in-service underwater submersible drone), and the name of the pilot.
It also includes written observations of the walls, floor, roof underside, seams, and outlet; notes on sediment, debris, and aquatic growth; still images pulled from the video; and the full video recording itself. Findings that point to deterioration are flagged so the owner can take them to the AHJ or a qualified contractor.
How to prepare for an in-service tank inspection
Find your last interior inspection report. The interval runs from the last documented interior inspection; if there is no record, plan as if one is due and ask the AHJ how it wants that handled.
Confirm the tank type and whether the interior has corrosion protection, since that sets the interval. Confirm safe access to the roof hatch, including ladders, platforms, and any keys or escorts. Let the AHJ and your monitoring company know an inspection is planned if they expect notice. Share any history of leaks, freeze problems, or past findings with FLOW when you request a quote.