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 man-

made 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 contamination9.4

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 low9.5

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

9.9

Figure 9-4 (A) Gravity-fed water distribution system. (B) A direct pump water distribution system. (C) A combination gravity-pumped water distribution system.

(A)

(B)

(C)

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

9.12

Figure 9-7 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

9.13

9.14

Figure 9-8 Dry barrel hydrant.

9.15

Figure 9-9 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

9.16

9.17

Figure 9-11 Schematic of dry hydrant installation.

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 above-

grade hydrant interferes with operations

• High-pressure hydrants connected to separate high-pressure water system

9.18

9.19

Figure 9-12 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– Interior valves, exterior protective devices

• Exterior systems require lock and key– Mostly found on privately owned property

9.20

9.21

Figure 9-13 External hydrant protective device.

Valves Associated with Water Distribution Systems

• Gate valves (butterfly valves) opened and closed to control water flow– Nonindicating 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

9.23

Figure 9-14 Hydrant with plumbing. Note the location of a gate valve between the water main and hydrant.

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

9.26

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.

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 withWater 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 nonflowing 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

avoided9.29

9.30

Figure 9-21 Atmospheric pressure being exerted on container of water.

9.31

Figure 9-22 Pressure is expressed in pounds per unit area (psi).

Testing Operability andFlow 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 Flowof 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 tests9.33

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

9.35

Table 9-1 Percentage Drop Measurements

Obstructions and Damage toFire 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