By Brian O’Connor, P.E.
All water-based fire protection systems have one thing in common, they need water. Without access to an adequate water supply these systems will not be function properly. When determining a water supply for fire protection, you need to make sure it is automatic (when required), reliable, and has sufficient volume and pressure to meet the system demand. Following is a review of options for water sources to supply a water-based fire protection system.
Connection To Public Water Supply
Commonly referred to as a waterworks system, this is typically a connection to a water main at the street level. These can be controlled or operated by a municipal or private water company.
A connection to a public water supply is acceptable only if a water flow test or other approved method determines that volume exceeds peak demand. The pressure also needs to exceed the peak demand but that can be increased by installing a fire pump.
The water supply tested should represent the supply that might be available at the time of a fire (in other words, at times of highest demand on the waterworks system and at times of the lowest demand on the waterworks system). This is critical because public water supplies can fluctuate widely from season to season and even within a 24-hour period. These can also be affected by things such as drought, interruptions caused by flooding, or ice in winter. Some cities are also dropping delivered system pressure as a means of water conservation. A system that is designed without taking into account fluctuations in the water supply could result in insufficient pressures or over pressurization of the system.
Water storage tanks are tanks that supply water for water-based fire protection systems. Water tanks can be used for several different scenarios but most commonly they are used where an adequate supply of water is not available or reliable. There are several types of tanks that can be used as a water supply such as gravity tanks, suction tanks, and pressure tanks.
Gravity tanks are elevated water tanks that utilize gravity to provide pressure. They might be capable of providing the necessary pressure to operate a fire suppression system on their own, or they can be used to provide water to a fire pump. Gravity tanks are not typically used in private water supplies, but they’re a common part of a reliable waterworks system.
Suction tanks are mounted on the ground or below ground. Because of this they do not utilize elevation as a primary means to increase the pressure. Suction tanks typically provide water to a fire pump, which then boosts the pressure. Special consideration is needed for below grade tanks because they must either have a vertical turbine pump or a pump located below the tank.
Pressure tanks contain both water and air under pressure. When a system is actuated, the pressurized air pushes the water out of the tank. Because of this, a sufficient capacity of air must be available to discharge the water from the tank at the necessary rate. Pressure tanks are rarely used because they are typically no larger than 10,000 gallons (37,850 liters).
Penstock, Flume, River, Lake, Reservoir
Naturally occurring sources include penstocks, flumes, rivers, ponds, and lakes. Water supply sources such as these must be arranged to avoid mud and sediment being introduced into the fire protection system piping. These are thus required to include double removable screens or strainers on the water piping intakes. Their reliability and ability to meet system demand must also be verified and potential seasonal fluctuations taken into consideration. These naturally occurring sources need to be installed with a fire pump to provide adequate pressure for the system. The authority having jurisdiction (AHJ) should be consulted when considering the use of these types of water supply sources.
Recycled Or Reclaimed Water
There is an increased interest in using recycled or reclaimed water as a potential water supply for fire protection systems, such as sprinkler systems, due to increased interest in sustainable water usage, and changes in weather patterns that result in drought. The source of the water and the treatment process (if any) must be analyzed to determine that any materials, chemicals, or contaminants in the water will not be detrimental to the components of the sprinkler system it contacts.
Several of the water supplies discussed above utilize fire pumps to increase pressure. It’s important to understand that fire pumps cannot create more water than is available from a given source. As such, fire pumps on their own are not an acceptable water supply. They may be necessary, however, to make a water supply acceptable by increasing the available pressure.(For information on the different types of fire pumps see this April 2021 blog post from NFPA on fire pump types.)
Acceptable sources of water for a fire pump include reliable waterworks, water storage tanks, penstocks, flumes, rivers, ponds, lakes, or any combination of these as long as the supply into the fire pump has sufficient volume to meet the system demand.
There are several other considerations that can help in the decision-making process of selecting an appropriate water supply, including the following:
- Corrosion. It is important to make sure the water supply doesn’t have any corrosive properties
- Zebra Mussels/Microbiological Corrosion, or other harmful animal life. These can severely limit the flow of water though your system or affect access to the water supply.
- Dirty Water. Mud and debris in the water will have a negative effect on the system.
- Pressure Variances. It is important to ensure your system takes into consideration the possible pressure variances caused by droughts, flooding, freezing, and usage of the water supply by others.
- Automatic Water Supplies. Most water supplies are required to operate without human intervention.
- Reliability. Water supplies need to be able to supply water at any time. Multiple water supplies are not required but could increase the reliability of your water.
In conclusion there are several different options for water supplies. Depending on the needs of the system that the supply is supporting and the geographical and topographical location of the building, the type of supply that is available will vary.
O’Connor is an Engineer in the Technical Services department at the National Fire Protection Association (NFPA) and President for the New England Chapter of the Society of Fire Protection Engineers. A professional engineer registered in the states of Texas and Massachusetts, O’Connor earned his Bachelor’s Degree in Mechanical Engineering from Rowan University and a Master’s Degree in Fire Protection Engineering from the University of Maryland. At NFPA, he focuses on topics such as aviation, portable extinguishers, water based fire protection, energy storage systems, and healthcare facilities.