Water Supplies for Fire Protection: City, Tank, Pond, Well

However well your sprinkler system is designed, if the water supply is insufficient, the system collapses during a fire. NFPA 13 is clear: the sprinkler system must connect to a water supply that delivers the calculated flow and pressure for the full operation duration. Five main supply types exist globally — each with its own advantages, risks, and NFPA rules.

1. Public Water Main (City Supply)

The most ideal source: direct feed from municipal piping. Most US and European cities support this. Status in Turkey?

• Advantage: Unlimited volume, no maintenance, no tank upkeep.
• Disadvantage: City pressure can be low/variable. Pressure drops further during a fire.
• NFPA requirement: Flow test required every 20 years to verify capacity.

In Turkey: Some central districts of Istanbul/Izmir/Ankara are adequate. Rural areas and industrial zones are insufficient. Written pressure/flow guarantees from the local water authority are essential.

2. Underground Tank + Pump

The most common solution in Turkey. Reinforced concrete or plastic tank below the building, with an NFPA 20-listed fire pump above.

• NFPA 22 rules: Tank partitioned, with drain and overflow outlet. Sprinkler and potable water separate (AWWA rules).
• Calculation: Sprinkler flow × operation duration + hose allowance × duration. Light Hazard 30 min, OH 60 min, EH 90+ min.
• Typical size: Hotel 40-80 m³, mall 100-200 m³, industrial 300-1000+ m³.

3. Elevated Tank

Common in the US, rare in Turkey. A water tank elevated atop the building or on a tower in the adjacent area. Advantage: gravity provides sufficient pressure, reducing pump requirements. Disadvantage: freeze risk, structural load, earthquake sensitivity.

In Turkey: Seen in petroleum refineries, industrial complexes, some older airports. NFPA 22 separately governs seismic design of elevated tanks.

4. Natural Source (Pond, Reservoir)

A pond or constructed reservoir adjacent to a factory or industrial site. Critical for facilities requiring large water volumes (especially against storage fires).

• NFPA requirement: Calculate minimum usable volume and dedicate a pond section covering this quantity.
• Dry hydrant: Freeze-resistant line running underground from pond to hydrant. Fire department connects here and draws water.
• Flow verification: Annual NFPA 25 flow test confirming flow/pressure.

In Turkey: Tekirdağ industrial zones, Kocaeli refinery region, some organized industrial districts plan for natural sources.

5. Well

The rarest, but occasionally mandatory source. Deep well water drawn via electric pump.

• Critical problem: Well flow is usually low (200-500 L/min). Can't meet sprinkler system demand directly.
• Solution: Well + large underground tank combination. Well slowly fills the tank; the fire pump draws from the tank during a fire.
• NFPA 24: Well pumps are regulated separately as listed fire pumps or water supply pumps.

Hybrid Systems

In reality, most facilities use multiple sources:

• City + backup tank: Tank activates when city supply fails
• Well + tank: Well fills tank; tank serves the fire
• Pond + pump + tank: All sources combined in large industrial facilities

Water Supply Flow Testing

NFPA 25's core requirement: water supply must periodically verify the flow/pressure it provides:

• Hydrant flow test: Pressure/flow the sprinkler system receives from the city.
• Pump flow test: Fire pump's conformance to NFPA 20 curve.
• Tank inspection: Annual check of volume inside the tank.

Water tank and pump sizing in SprinkCalc + MEP Calc

NFPA 13 water demand, operation duration, tank sizing — in SprinkCalc. NFPA 20 pump selection in MEP Calc.

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Common Mistakes in Turkey

1. Closing out projects without a city flow test: "City water is available" assumption; halfway through the project, pressure turns out to be insufficient.
2. Sizing tank without including hose allowance: Sprinkler flow + hose allowance go together.
3. Mixing potable and fire water in one tank: Prohibited under AWWA and NFPA 22. Separate tanks or isolation valves required.
4. Direct well-to-sprinkler pumping: Flow insufficient; a tank is always needed.

Conclusion

Water supply selection is the foundation of whether a sprinkler system actually works. The underground tank + NFPA 20 pump combination — most common in Turkey — is the right choice as long as tank volume and pump curve are calculated per NFPA. For rural industrial facilities, ponds and wells become alternatives, but each must follow its specific NFPA standard.