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
– Measured over an area
• 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
– Water cools the fuel below its ignition
temperature
9.2
Sources of Water Supply
• A wide range of natural and manmade factors affects 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
9.3
Groundwater
• Most of Earth’s freshwater supply is
groundwater
– Seeps into the ground from rain and other
sources
– Collects in aquifers
– Permeates into layers of water-bearing soil
• 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
– Less chance of contamination
9.4
Surface Water
• Almost 75 percent of the Earth covered
with water
– Most found in oceans and seas
• 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 40-foot difference between
high and low
9.5
Mobile Water Supply Apparatus
• Water tank on fire apparatus supplies the
water
– Small fires and fires in areas without water
distribution system
• 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 250 gpm
– Fire pump of at least 750 gpm
– Transfer pump of at least 250 gpm
9.6
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
9.7
Water Distribution Systems
• Components of water distribution system:
– Method of getting the water
– Filtration, treatment processes
– Storage, supply, and distribution
• Small groundwater systems require a well
with pumping station
• Large well systems: multiple supply,
processing, storage units with massive
feeder lines
• Water supplied in three ways: gravity fed,
pumped, combination
9.8
(A)
(B)
(C)
Figure 9-4 (A) Gravity-fed water distribution system. (B) A
direct pump water distribution system. (C) A combination
gravity-pumped water distribution system.
9.9
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
9.10
Wet Barrel
• Water in the barrel up to valves of each
outlet
– Used in areas not subject to freezing
• 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
9.11
Figure 9-7 Typical schematic of wet barrel hydrant.
9.12
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
9.13
Figure 9-8 Dry barrel hydrant.
9.14
Figure 9-9 Typical schematic of dry barrel hydrant.
9.15
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
9.16
Figure 9-11 Schematic of dry hydrant installation.
9.17
Specialty Hydrants
• Wall hydrants mounted on wall of a
building
– Be sure to connect to wall hydrant and not the
fire pump test connection outlet
– Direct connection to water supply system
• Flush-type hydrant mounted below grade
level
– Found in a pit, vault, or valve box
– Allows access to water source where abovegrade hydrant interferes with operations
• High-pressure hydrants connected to
separate high-pressure water system
9.18
Figure 9-12 Wall fire hydrant.
9.19
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
– Interior valves, exterior protective devices
• Exterior systems require lock and key
– Mostly found on privately owned property
9.20
Figure 9-13 External hydrant protective device.
9.21
Valves Associated with
Water Distribution Systems
• Gate valves (butterfly valves) opened and
closed to control water flow
– Non-indicating gate valves installed at:
• Interconnections of water mains
• Intermediate points of long sections of water
mains
• Before each hydrant and major building
connection
• Check valves control water flow in one
direction
• Backflow preventers: check valves that
prevent backflow of water from one system
into another
9.22
Figure 9-14 Hydrant with plumbing. Note the location of a
gate valve between the water main and hydrant.
9.23
Rural Water Supply
• Rural water supply can occur anywhere
• Urban and suburban areas often have
places where hydrants are too far away
– Limited access highways, large bridges
• Require careful coordination and control
• Water supply group supervisor part of
incident command system
– Full authority over water apparatus operations
• Firefighters assigned to water supply are
vital
9.24
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
– Capacity equal or greater than its tank size
– Collapsible or inflatable tanks set up next to
engine
• Jet dump speeds unloading of tanks
• Multiple tanks using a jet siphon set up
together
9.25
Figure 9-15 Portable water tanks
are an essential piece of
equipment for shuttle operations.
Figure 9-17 Tender at
dump site dropping water
directly into portable tank.
9.26
Mobile Water Apparatus
Operation
• Shuttle operation involves moving water
between dump site and fill site
• Dump site: where water delivered for quick
unloading
– Set up first
• Fill site: location of water source
– Optimum fill site allows vehicles to drive through
• Shuttle operations time cannot be
decreased by increased vehicle speed
9.27
Pressure Associated with
Water Distribution Systems
• All Earth’s water under pressure
– Atmospheric pressure: 14.7 pounds per
square inch
• Atmospheric pressure reduces 0.5
psi per 1,000 feet of elevation
• Pressure in non-flowing closed
system equal at all points
– While flowing, reduced by friction and
loss of pressure at opening
9.28
Pressure Associated with
Water Distribution Systems
(cont’d.)
• Distribution systems supplied under
pressure
– System pressure never as high as firefighters
prefer
• 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
9.29
avoided
Figure 9-21 Atmospheric pressure being exerted on
container of water.
9.30
Figure 9-22 Pressure is expressed in pounds per
unit area (psi).
9.31
Testing Operability and
Flow of Hydrants
• Regular testing identifies inadequate
hydrants
– Coordinated between fire and water
departments
• Operability testing:
– Wet and dry hydrants:
• Visual inspection for damage
• Ensuring hydrant valve closed
• Remove all caps, check threads and
gaskets
• Check that all valves allow water to flow
9.32
Testing Operability and
Flow of Hydrants (cont’d.)
• Operability testing (cont’d.):
– Dry barrel hydrant:
• Ensure drain valve working
• Determine water level dropping after hydrant
shut off
• Visual inspection of piping, caps, gaskets
• Flow test followed by backflushing of the
hydrant
– Replace caps, oil moving parts, and paint the
hydrant
• Fireground method for flow tests
9.33
Determining Static, Residual,
and Flow Pressures
• Connect a pumper to a hydrant and turn it
on
• Static pressure: pressure in the system
with no hydrants or water flowing
• Charge the first line with desired volume
– Check compound gauge for residual pressure
– Compare percentage of pressure drop from
static to residual
• Second test involves multiple hydrants
– Not conducted during fire operations
9.34
Table 9-1 Percentage Drop Measurements
9.35
Obstructions and Damage
to Fire Hydrants and Mains
• Obstructions and damage can occur to
fire hydrants and water mains
– Small leaks develop as water system matures
– Vandals damage by opening or closing valves
– Opening valve in freezing weather without
allowing water to flow may cause hydrant to
freeze and crack
– Accidents can crack pipes or break off a
hydrant
• Firefighters should ensure hydrant is
opened or closed fully
9.36
Lessons Learned
• Water is the most common fire
extinguishing agent
– Must be supplied in sufficient quantity
• 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
9.37