WATER SUPPLY
1. General Design Concept of External Water Reticulation System
1.1 Reference
The water reticulation system shall be design in compliance with:
Uniform technical guideline Water Reticulation & Plumbing by SuruhanJaya
Perkhidmatan Air Negara (SPAN)
Lembaga Air Perak (LAP)
Standard Specifications for Building Works 2005 – By Jabatan Kerja Raya (JKR)
1.2 Source of Water Supply
Rivers are the main source of raw water for Lembaga Air Perak. Of this, main supply comes
from Perak River. It supplies more than 40% of the total needs without the extraction of
ground water. For this project, the main water source shall be from the proposed elevated
water tank to be included with the project’s water supply system as depicted in the figure
2 below and water supply will be tapped, from an incoming main pipe laid along A164
Jalan Manong to the elevated water tank and with the use of gravity, the water will be
distributed to each bungalow. Pressure head from main pipe assumed to be 60m.
Figure 1 : Red Mark represents the proposed project site.
Figure 2 : Proposed Elevated Water Tank Location and Water Supply Pipe Layout
1.3 Water Demand 1.3.1 Water Demand Estimation
Based on Malaysia JKR Standard, the water demand formula for typical housing estate is as
follows:
W = ∑ (N x C) x F + Da
Where:
W = Average daily water demand
N = Number of type of houses(units)
C = Cost per unit consumption
Da= Additional water demand
The total water demand for the proposed development, is estimated according to the type
of development, the number of units of area allocated:
Avg. Daily Water Total Water
Type of Building Quantity
Demand (L/d) Demand (L/d)
Bungalow 8 2,000 16,000
Swimming Pool 8 17,000 136,000
Total 152,000
1.3.2 Service Factor
The service factor is the potential percentage of population served. For instance, the
water distribution system cover 90% of the area will give a service factor equals to 0.90,
but it does not necessarily mean that 90% of the populations in the area have service
connection. Service factor vary from state to state and also district to district. For the
project, service factor of 1.0 is used means that water is supplied to all the
house/buildings.
1.3.3 Provisional for Additional Water Demand
Fire flow requirement must be considered for the design purpose. Referring to Table
2.1 which is outlined in the JKR Standards as Table 14.18, the recommended risk
category of fire flow requirement is Class D with average required flow of 1140
litre/min and the maximum number of hydrant outlets used simultaneously in one unit.
1.3.4 Total Water Demand with Additional Water Demand
The total water demand that shall be supplied is as follow:
Total Water Demand = Water demand for project + Fire Flow requirement
1140𝑙 60𝑚𝑖𝑛 24ℎ𝑜𝑢𝑟
=152,000 +( × × )
𝑚𝑖𝑛 ℎ𝑜𝑢𝑟 𝑑𝑎𝑦
= 1,793,600 litres/day
1.3.5 Dominant Flow
Dominant flow should be implemented in the water reticulation analysis. The peak
flow shall be 2.5 (SPAN : Part B, Section C : Hydraulic Requirements (i)).
Case 1 (Fire Flow) = Water demand for project + Fire flow
Case 2 (Peak Flow) = Water demand for project x Peak Factor
Thus,
Case 1 = 1,793,600 litres/day
1
= 1,793,600 litres/day x( 24 x 3600 )
= 20.76 litres/sec
Case 2 = 1,793,600 litres/day x 1.25
1
= 4,484,000 litres/day x( 24 x 3600 )
= 51.90 litres/sec
1.4 Land Reserves for Elevated Water Tank
Land reserves with minimum dimension of 55 x 55 (referring to Minimum site dimension
for construction of elevated water tank (SPAN: Part B, Table B.4) is required to
accommodate elevated water tank and shall be adequately sized to provide for vehicular
access, building setbacks and to allow for inspection and maintenance of the facilities.
However, these dimensions exclude areas of offices, storeroom, toilet or quarters as it
would a site for mostly maintenance.
Figure 3 : Minimum Site Dimensions for construction of service reservoir (SPAN : Part B, Table B.4)
2. Design Concept of Elevated Water Tank
Justification Calculation
To pressurize a water supply system
for the distribution of potable water,
Purpose
and to provide emergency storage for
fire protection.
The elevated water tank capacities = 1,793,600 × 0.8
Capacities
must be around 80% of using factor. = 3,587,200 Litre / day
1 Litre = 0.001 m3
Minimum volume of water
needed to be store in storage tank
= 3,587,200 Litre/day × 0.001 m3
The height of water tank is assumed to
= 3,587.2 m3
Design be around10 meter and the water tank
Length 18 meter
will be in rectangular shape.
Width 16 meter
Height 14 meter
= 18m × 16m × 14m
= 4,032 m3 > 3,587.2 m3
Height – 10 m
Figure 4 :Proposed design of elevated water tank
Height of the elevation is designed to be 10 meter above ground level to provide
pressure with use of gravity to distribute water to each bungalow without any
disruptions.
2.2 Design Criteria of Pump Station
Type of pump used in this project is centrifugal/kinetic pump that is designed to convert
mechanical energy into hydraulic energy. Water is supplied from delivery line, into utility
space and then the internal plumbing system. For water to reach elevated water tank require a
separate pumping system in order to create sufficient pressure.
2.2.1 Pump Design
The steps and procedure to follow to select a centrifugal pump:
Determine the flow rate
Determine the static head
Determine the friction head
Calculate the total head
Select the pump
Parameter Unit Value
Density of Water, p kg/m3 1000
Gravity, g m/s2 9.81
Moody’s diagram, f - 0.28
Head Loss, h m 29.50
Length of the Pipe metre 10m
Flow, q m3/s Normal: 0.002
Peak: 0.0028
Velocity m/s Normal = 2.5
Peak Velocity = 1.0
Efficiency % 60
Head Loss,h
𝐿 𝑉2
HL = 𝐹 𝑥 (𝐷) 𝑥 (2𝑔)
135𝑚 (1.75)2
= (0.28 𝑥 ( ) 𝑥 ( 2𝑥9,81 )
0.2
= 29.50
HL = Total Head Loss
F = Friction factor related to the roughness inside the pipe
L = Length of the pipe
D = Diameter of the pipe
V = Average liquid velocity in the pipe
2g = Two times the Universal Gravitation Constant
Hydraulic Power
𝑞𝑥ρ𝑥𝑔𝑥ℎ
Ph(kW) = ( )
1000
0.0028 𝑥 1000 𝑥 9.81 𝑥 29.5
=( )
1000
≈ 0.81
Shaft Power
Ph
Ps(kW) = ( η )
0.81
= ( 0.6 )
≈ 1.35
Pressure needed to pump up to 10m (elevated water tank height):
P = ρ𝑔ℎ
= 1000 x 9.81 x 18
= 176,580 N/m2
In this project, the value of hydraulic power and hydraulic shaft is small because an elevated
water tank have been built nearby Kampung Senggang. By considering the design
calculations and condition, a pump needs to be proposed so that the water distribution can be
done smoothly. Since the hydraulic and shaft power is manageable, so a single centrifugal
water pump with a total head of 34m can be applied. A pump shall we installed at ground
level at the suction tank resulting in enough pressure to distribute water to each floor.
3.0 Pipeline Routing
The pipes connecting the pump are classified under TWO categories:
Communication Line: Suction tank to Centrifugal pump
Delivery Line: Centrifugal pump to Rooftop water storage tank
Considerations Justification Reference
Most of the pipes are Provide easy access for maintenance
laid adjacent to or Avoid laying pipes directly under the
underneath roads roads, minimize the traffic loading acting
on the pipes, hence reduce materials to SPAN
bury the pipes.
Reduce cost of bedding the pipe
Pipelines shall not be laid beneath a road
pavement unless so permitted by the
Commission / Certifying Agency.
Water pipes shall not Minimize the risk of contaminating water
be laid below sewers supply.
and away from any A minimum vertical clearance of 1.0m
other utilities and shall be provided between the crown of a SPAN
also from drains. sewer pipe and the bottom of a water pipe.
The horizontal clearance between sewer
and water pipelines shall be 3.0m where
applicable.
3.1 Water Pipeline Distribution System Selection
Referring to the (SPAN: B4 Design Criteria), the design criteria for external reticulation
networks and supply mains are:
i) Water quality to not get deteriorated in the distribution pipes
ii) Supplying water at all the intended places with sufficient pressure head.
iii) Take into consideration the construction of pipelines in rocky, waterlogged or
compressible ground
iv) Supply the requisite amount of water during fire fighting
v) Repair and maintenance should be done without any disruption to the water supply
vi) Should be water -tight and laid 1 metre measured above crown of the pipe
vii) Carry out survey and site investigation to check for utilities lying adjacent to or
crossing the line of planned water pipeline trench.
3.2 Selection of Pipe Material Criteria
Pipe materials for supply mains and external reticulation pipelines shall be selected based on
laying conditions, whether in corrosive soils or otherwise; under different terrain conditions;
or if subjected to traffic loadings or not. The soil investigation reports show a moderate
corrosive soil. After comparing several options of piping material to apply in the project’s water
system, we narrowed the options down to two different material after consideration such as
initial cost, operation/maintenance cost, expected life and most importantly, its purpose served
or compatibility to existing site conditions such as feasibility or environmental conditions.
Referring to SPAN (Table B.6.1, Table B.6.2 and Table B.6.3), the most durable and
commonly used pipe material is HDPE with diameter 200mm and roughness of 0.00015
(Darch-Weisbach). Being widely used in piping systems worldwide, HDPE pipes will be used
for all the pipelines that shall be lad for this project. There are number of reasons why, which
are:
Corrosion Resistance:
The HDPE Pipe does not rust, rot of corrode. It is resistance to biological growth and
has extended service life and long-term cost savings.
Fatigue resistance:
HDPE pipe is flexible and ductile, not rigid allowing it to have outstanding resistance
to fatigue.
Leak free joints:
Traditional infrastructure piping is joined with bell and spigot or mechanical type of
joint but HDPE can be joined with heat fusion to produce permanent leak free joint.
Eco-friendly:
It takes less energy to manufacture HDPE than non-plastic pipes. HDPE is lightweight
and is often most cost effective to transport than metal pipes.
Extended service life:
HDPE pipe is a safe and durable product ideal for your piping infrastructure. The
service life of HDPE is estimated to be between 50 to 100 years, depending on
application, design and installation.
3.3 Pipe Network Design Calculation
Parameter Unit Value
Density of Water kg/m3 1000
Gravity m/s2 9.81
Minor Loss Coefficient K (loss) 90deg 0.3
K (loss) Tee 0.2
K (loss) 180deg 0.2
Roughness HDPE 0.0015
Reynolds Number of water 21978 (Turbulent Flow)
Moody’s diagram, f 0.28
Diameter of Pipe M 0.2
Flow m3/h 113.12
Velocity m/s 1.0
π 3.142
Pipe diameter are constant throughout the project site
Reynold’s number assumed to be 20000 (Turbulent flow inside pipe)
Does not include per house fixtures (bathtub, sink, shower, etc)
Reynolds Number:
𝑝𝑣𝐿
𝑅𝑒 =
µ
1000(1.00)(0.200)
Re= 0.0091
Re = 21978 (Categorised as Turbulent Flow)
i) Laminar flow when R < 2300
ii) Transient flow when 2300 < R < 4000
iii) Turbulent flow when R > 4000
Flowrate (m3/h):
d 2
𝑄𝑤 = 3600π x v ( )
2
0.200 2
𝑄𝑤 = 3600π x 1.0 ( )
2
= 123.11m3/h
d : Pipe Inner Diameter (m)
v : Water Velocity (m/s)
Qw : Water Flow Rate (m³/h)
Head Loss,h
𝐿 𝑉2
HL = 𝐹 𝑥 (𝐷) 𝑥 (2𝑔)
337.5𝑚 (1.75)2
= (0.28 𝑥 ( ) 𝑥 ( 2𝑥9,81 )
0.2
= 73.75
HL = Total Head Loss
F = Friction factor related to the roughness inside the pipe
L = Length of the pipe
D = Diameter of the pipe
V = Average liquid velocity in the pipe
2g = Two times the Universal Gravitation Constant
Parameter Unit Value
Density of Water, p kg/m3 1000
Gravity, g m/s2 9.81
Moody’s diagram, f - 0.28
Head Loss, h m 73.75
Length of the Pipe metre 337.5m
Flow, q m3/s Normal: 0.002
Peak: 0.0028
Velocity m/s Normal = 2.5
Peak Velocity = 1.0
