Fire sprinkler systems play a critical role in fire protection for many buildings. They can save lives and property when properly installed and maintained for the hazards they address. However, these systems are water-based and, therefore, rely heavily on having an adequate water supply. So, onto the discussion of water supplies, key requirements and details to ensure the water supply is available and ready.

Types of water supplies

To begin, many properties in the United States use a public water system to supply fire protection systems. Public water systems have many advantages as they are a utility relied upon in many jurisdictions. As a utility, they are held to a high standard of performance, which aligns well for use in supplying a fire protection system. 

Public water supplies are typically the simplest option, as the infrastructure is already in place, and the source is considered reliable and stable. Of course, they may not work perfectly for every building and fire sprinkler system installed, but they are a good starting point. In addition, they are potable water, which helps limit the amount of contaminants to meet state and federal guidelines.

When a public water supply is not available or not the desired option for the sprinkler system, then a private water supply would be used. This supply could be dedicated to a campus of buildings or a single fire sprinkler system. A private supply is comprised of private piping (not part of the water utility), open sources (e.g., ponds or lakes), wells or tanks. This allows for independence from the water utility, but can create additional maintenance in confirming the appropriate capacity and water quality over the system’s lifespan.

There can also be scenarios where a combination of public and private is used as the water supply. In some situations, redundancy is implemented in this manner, particularly in buildings where the water supply is critical.

It should be noted that confirming the water supply is part of the owner’s responsibility as declared by Section 4.2(4) in NFPA 13. For public water supplies, this also includes any necessary adjustments to the flow test data to account for supply fluctuations or safety factors. The jurisdiction’s water authority commonly guides the adjustments and could include, but is not limited to, peak demands, changes based on planned development, elevation changes and seasonal usage. Many larger jurisdictions also use modeling programs to predict water availability based on future conditions.

Water supply demands

After the water supply source is determined, it needs to be evaluated to determine if it can provide the fire sprinkler demand for the flow, pressure and duration expected for the supply. 

These values are all affected by the building’s occupancy and the hazards anticipated based on its use. For example, light hazard occupancies, such as offices or classrooms, require a 30-minute water supply, while ordinary hazard occupancies, such as retail shops, parking garages or mechanical rooms, need at least a 60-minute water supply. 

Obviously, this will vary the total volume required to be available for fire protection. It is important to note that with multiple water-based fire protection systems, the water supply must be able to meet the demand of any system individually. It is assumed that only one fire incident will occur at any given time.

For each water-based system protecting a space, the flow (gpm) and pressure (psi) are calculated where it connects to the water supply. The specific amounts will vary depending on the sprinklers or nozzles used, the pipe material and sizes, and the layout of that piping throughout the system, all the way back to the supply connection. 

The sprinkler or nozzle selected affects the amount of water based on how much is required for the hazard, along with the pressure needed to create the spray pattern. In addition, choosing the pipe diameters across the piping network will factor into the hydraulics of the system and the amount of pressure required in the water supply to meet that demand.

Layout technicians plan the fire protection system in accordance with the appropriate system standards, such as NFPA 13, Standard for the Installation of Sprinkler Systems. This also includes hydraulic calculations that allow the technician to refine the pipe sizes, ensuring that the water supply can meet the demand. As part of the installation standard, sprinkler systems must also account for water used by the responding fire department at the point of connection, such as a fire hydrant.

What happens when the existing supply does not meet the necessary demand? The water supply will need to be supplemented. This could be a scenario where the public water supply can provide the amount of water and duration needed for the system, but it cannot achieve the pressure. Here, a fire pump could be used to increase the pressure of the supply and meet the system demand. Another situation may be a building that requires a water storage tank to provide water for the fire protection system(s).

It is common to use a fire pump to supplement the water supply, whether public or private. These installations are commonly governed by NFPA 20, Standard for the Installation of Stationary Fire Pumps. When a pump is in place, it becomes a critical component in that water supply. Fire pumps come in different sizes to handle a wide range of flow needs, creating the necessary pressure so the water reaches the remote area of the sprinkler system. 

Water quality

Water is basic in fire protection, but the quality of that water can affect the systems, especially over time. Public water supplies are often considered the baseline, as the water is a potable source and regulated by water authorities. What are the concerns around water quality? Two of the top concerns are sediment carried in with the water and corrosion in the system from the water.

Sediment can enter the system and settle in the nooks and crannies within it, affecting the fire sprinklers. Fine sediment could settle and solidify at the sprinkler inlet, limiting water flow through the device should it operate. Larger sediment could pose a challenge by blocking water flow in smaller piping or at the inlet of a sprinkler. There is also the chance of larger sediment passing through a sprinkler and impacting the deflector, possibly altering the spray pattern. 

Where a known problem exists, filtration may be a solution. If open water sources are used, then required screens are in place to keep larger sediment, debris or even wildlife (fish, frogs, etc.) out of the system equipment and piping.

Water itself can cause corrosion when in regular contact with materials such as steel pipe. Corrosion is limited as the systems are not in regular operation. Microorganisms in the water could increase the corrosion rates of piping materials. The owner’s certificate also calls attention to this, stating, “Any special knowledge of the water supply, including known environmental conditions that might be responsible for corrosion, including microbiologically influenced corrosion (MIC),” (Section 4.2(5)). This should be shared so appropriate action can be taken as needed. 

In general, corrosion within systems takes a significant amount of time before it needs to be addressed, but it highlights the importance of periodic inspection, testing and maintenance to ensure that it is not a detrimental problem. 

Care should also be taken around any treatment used for the condition of the water. Although it may improve the water, there could be adverse effects on the system’s equipment or piping. Something as simple as high levels of chlorine in the water can speed up the oxidation of steel, which can create rust and, eventually, pits and leaks in the piping. 

Also, if additives are present in the water, compatibility must be confirmed to prevent inadvertent harm to devices, equipment and piping. This would also apply if recycled or reclaimed water is used, as there are many variables regarding where the recycled or reclaimed water originated.

Inspection, testing and maintenance

In general, water-based fire protection systems follow NFPA 25, Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems. This applies to any of the fire protection systems and supply lines not under the jurisdiction of a public water authority. Periodic reviews confirm that the system operates as intended, with tests included to demonstrate that the expected water is available to the system should there be a fire incident. 

Technologies are now implemented to aid in monitoring water levels, so if action is needed, it can be handled in a timely fashion. Inspection, testing and maintenance cannot be stressed enough as reviewing system components for their functionality keeps the system working.

Future considerations

When planning the fire sprinkler system, many of the details and thoughts are about the present moment and use of the building. However, it is also important to think ahead as most systems will be in place for many years. Considerations related to water supply may include future water conditions and availability, especially in developing areas. 

For example, if a new manufacturing facility is built nearby and has high water demands for its regular operations, does this alter the amount available for existing fire protection systems in the area? Unfortunately, no one-size-fits-all answer exists. Hopefully, local authorities are monitoring growth and development to aid existing building owners in keeping their property and occupants safe.

Another topic that has continued to arise in recent years is climate change. As weather patterns change and global warming continues, the amount of water available can change, too. This may be more prevalent in open sources of water, such as a drought affecting the level of a pond that supplies the fire sprinkler systems for a campus of buildings. 

This change will not be seen overnight, as it often takes many years to make a significant difference. However, as the existing stock of buildings continues to age, confirming the water supply is crucial to the proper performance of its water-based systems.

Without water, no fire sprinkler system will work. The water supply is relied on heavily to protect lives and property every day. Understanding the source of water and the components needed to deliver it to the fire sprinklers is key. Each system — fire sprinkler, standpipe, fire pump, etc. — requires detailed knowledge for both installation and ongoing maintenance.

Every building owner wants to achieve longevity for their fire sprinkler system and its water supply. Keeping an eye on the water supply and its components will provide the best outcome should the fire sprinkler system be called into action.

AFSA News

Looking to expand your knowledge on water-based fire protection systems? Webinars are a great way to learn about a specific topic from the convenience of your desk. AFSA provides more than 20 webinars each year, and they are free for AFSA members (nonmembers can attend for a nominal fee). 

Two webinars remain in 2025: November 12, Design Area Adjustments in NFPA 13, and December 3, Neglected Chapters in NFPA 25. Visit www.firesprinkler.org/webinars to view the sessions offered, including the 2026 schedule, and register for any or all the live events.