Chapter 9 Water Supply

Introduction Water supply is one of the most critical elements of firefighting. Water supply dictates the fire flow capacity. Pressure is the force of water. Fire flow requirement is the amount of water required for putting out the fire. Water’s ability to absorb large quantity of heat makes it effective in fighting fire.

Sources of Water Supply A wide range of natural and man-made factors affect water sources. Water in a constant cycle of change Sun evaporates water into atmosphere. Condenses into clouds Eventually falls as rain Some areas alternate between rainy and dry seasons. Some areas have plenty of water, but it is frozen.

Groundwater Most of Earth’s freshwater supply is groundwater. Water table: level of water under Earth’s surface Springs are groundwater sources that flow to the surface. Shallow wells prone to changes in water table Deep wells more predictable

Surface Water Almost 75% of the Earth covered with water Man-made surface sources include lakes, ponds, reservoirs, swimming pools, water tanks. Tidal changes are rising and falling of surface water levels. Due to gravitational effects between Earth and moon May be as much as 12-metre (40-foot) difference between high and low

Mobile Water Supply Apparatus Water tank on fire apparatus supplies the water. Water tender: mobile water supply apparatus Tenders combined with portable water tanks provide large volumes of water to fireground. Tenders may have small booster pump of at least 1,000 Lpm (250 gpm), fire pump of at least 3,000Lpm (750 gpm), or transfer pump of at least 1,000Lpm (250 gpm)

Tanks, Ponds, and Cisterns Water tanks May be underground, ground level, elevated May have a dry hydrant or other connection, or just a drafting point Ponds may be developed for fire protection. Lined or unlined, with or without dry hydrants Cistern: underground tank made from rock or concrete

Water Distribution Systems Several components Small groundwater systems require wells with pumping stations. Large well systems: multiple supply, processing, storage units with massive feeder lines Water supplied in three ways: gravity fed, pumped, combination

(A) (B) (C) (A) Gravity-fed water distribution system. (B) A direct pump water distribution system. (C) A combination gravity-pumped water distribution system.

Fire Hydrants Fire hydrants allow access to water supply systems. Two major hydrant types Wet and dry barrel hydrants Dry hydrant: pipe system for drafting from static water source

Wet Barrel Used in areas not subject to freezing Water in the barrel up to valves of each outlet Allows each outlet to be controlled by separate valve Additional lines taken off or supplied if outlet available Additional connection does not require flow through other outlets to be stopped Main control valve controls flow to all outlets.

Typical schematic of wet barrel hydrant.

Dry Barrel Used in areas where freezing temperatures could damage the hydrant Valve at base controls water flow to all outlets Base and valve below ground at water main Entire hydrant shut down to connect additional lines Operation in partially open position undermines the hydrant and ground Imminent damage to roads and buildings

Dry barrel hydrant.

Typical schematic of dry barrel hydrant.

Dry Hydrant Not really a fire hydrant Connection point for drafting from a static water source such as a pond or stream Pipe system with pumper suction connection at one end and strainer at other Primarily used in rural areas with no water distribution system May be found in urban or suburban areas as backup water supply

Schematic of dry hydrant installation.

Specialty Hydrants Wall hydrants mounted on wall of a building Flush-type hydrant mounted below grade level Found in a pit, vault, or valve box Allows access to water source where above-grade hydrant interferes with operations High-pressure hydrants connected to separate high-pressure water system

Wall fire hydrant.

Hydrant Protective Devices Devices or valves designed to protect the water system Most hydrants connected directly to domestic water supply Many water suppliers added measures to protect water supply. Exterior systems require lock and key.

External hydrant protective device.

Valves Associated with Water Distribution Systems Gate valves (butterfly valves) are opened and closed to control water flow. Non-indicating gate valves Interconnections of water mains Intermediate points of water mains hydrant and major building connection Check valves control water flow. Backflow preventers are check valves that prevent backflow of water from one system into another.

Hydrant with plumbing. Note the location of a gate valve between the water main and hydrant.

Rural Water Supply Rural water supply can be anywhere. Urban and suburban areas often have places where hydrants are too far away. Require careful coordination and control Water supply group supervisor should be part of incident command system with full authority over water apparatus operations. Firefighters assigned to water supply are vital.

Portable Water Tanks Mobile water supply apparatuses must quickly offload water and return to fill site. Each mobile apparatus should have a portable water tank with capacity equal to or greater than its tank size. Jet dump speeds unloading of tanks. Multiple tanks using a jet siphon set up together in larger operations

Tender at dump site dropping water directly into portable tank. Portable water tanks are an essential piece of equipment for shuttle operations. Tender at dump site dropping water directly into portable tank.

Mobile Water Apparatus Operation Shuttle operation involves moving water between dump site and fill site. Dump site: where water delivered for quick unloading Fill site: location of water source Shuttle operations time cannot be decreased by increased vehicle speed.

Relay Pumping Two or more pumps to move water over a longer distance than normal Water is discharged from one pumper to another pumper's intake to increase pressure. Determine if the water source is capable of supplying and maintaining flows and pressures.

Relay Pumping (cont.) Determining the number of pumpers in the relay operation Calculate the distance between pumpers Fire flow required on scene How close is the water source to the scene How much and what size of hose is being used How large are the pumpers in terms of flow ratings

Pressure Associated with Water Distribution Systems All Earth’s water under pressure Atmospheric pressure reduces 3Kpa for every 300 metres (0.5 psi per 1,000 feet) of elevation. Non-flowing closed system: pressure equal at all points but while flowing is reduced by friction and loss of pressure at opening Open system: subject to atmospheric pressure

Atmospheric pressure being exerted on container of water.

Pressure is expressed in pounds per unit area (psi).

Pressure Associated with Water Distribution Systems (cont.) Distribution systems supplied under pressure Pressures below recommended low residual pressure create a vacuum in part of the supply. High-flow and/or high-pressure areas are an advantage. Low-flow and/or low-pressure areas should be avoided.

Lessons Learned Water is the most common fire extinguishing agent. Supplying water requires understanding of the water source and the valves and hydrants. In areas with no distribution system, create one. Difficult to sustain adequate fire flow with mobile apparatus