NFPA 25 — Water Storage Tanks

NFPA 25 Chapter 9 applies to all water storage tanks that serve as part of a building's fire protection water supply. These tanks ensure an adequate and reliable water source is available when sprinkler systems, standpipes, or fire pumps activate during an emergency.

• Ground-level steel tanks — Welded or bolted steel tanks at grade, typically ranging from 5,000 to 500,000 gallons. Common in commercial and industrial fire protection systems.
• Elevated steel tanks — Pedestal, column-supported, or tower-mounted tanks that provide gravity-fed water pressure without a fire pump. Capacity typically 5,000 to 100,000 gallons.
• Rooftop gravity tanks — Wooden or steel tanks installed on building rooftops, particularly common in older New York City buildings. Provide gravity pressure to upper floors and supplement fire pump systems.
• Pressure tanks — Sealed tanks partially filled with water and pressurized with air. Used where elevated tanks are not feasible and provide immediate water pressure upon system activation.
• Concrete reservoirs and cisterns — Underground or partially buried concrete tanks serving as fire protection water storage, often found in campus-style or industrial settings.
• Wooden tanks — Stave-constructed tanks with steel hoops, common as rooftop tanks in the northeastern United States. Require specialized inspection for stave condition, hoop tension, and joint integrity.

Tank heating systems prevent the water supply from freezing and becoming unavailable during cold weather — a critical concern for buildings in the tri-state area where winter temperatures regularly drop below freezing for extended periods.

• Heating system types — Common tank heating methods include internal steam coils, electric immersion heaters, external tank blankets, and circulation heating systems that draw water through a heat exchanger and return it to the tank.
• Temperature monitoring — NFPA 25 requires that water temperature in the tank not drop below 40°F (4.4°C). Install temperature monitoring with low-temperature alarms that report to a continuously attended location or supervisory monitoring service.
• Annual testing — Before the first freeze of the season, verify heating system operation by activating the system and confirming temperature rise. Inspect steam coils for leaks, electric heater elements for continuity, and thermostatic controls for proper calibration.
• Redundancy — For tanks in areas with severe winter conditions, consider backup heating systems. A single heater failure during a prolonged cold snap can freeze an entire tank within 48 to 72 hours depending on tank size and insulation.

Thorough documentation transforms a routine inspection into a defensible compliance record. Every inspection should produce a report that includes the following elements:

• Tank identification — Record tank type, material, capacity, manufacturer, year of installation, and location. Include a unique asset identifier that ties to the building's equipment management system.
• Inspection findings — Document each item inspected with a pass, fail, or needs-attention status. For deficiencies, include photographs, measurements (such as coating thickness or sediment depth), and a severity rating.
• Recommended actions — Prioritize deficiencies by criticality. Immediate action items (such as a stuck control valve or non-functional heating system) should be distinguished from planned maintenance items (such as recoating in the next cycle).
• Historical comparison — Compare current findings to previous inspection reports to identify deterioration trends. Progressive corrosion, increasing sediment accumulation, or recurring heating system issues indicate the need for capital planning.
• Compliance status — State whether the tank meets NFPA 25 requirements or is deficient. For deficient tanks, provide a timeline for corrections and any interim measures needed (such as increased inspection frequency or temporary water supply arrangements).

Inspection reports should be retained for the life of the tank and made available to the Authority Having Jurisdiction (AHJ) upon request. Digital records with photo attachments are strongly preferred over paper-only documentation for long-term accessibility and searchability.