The document discusses water supply systems including water transmission and distribution. It describes the key components and design considerations for extracting, treating, storing, pumping and conveying water from its source through treatment, transmission, storage, and distribution to end users. The transmission system conveys treated or untreated water from sources to the distribution system through treatment plants and storage reservoirs using pipelines, tunnels, canals or aqueducts. The distribution system then supplies adequate water at sufficient pressure to individual consumers through a pipe network with valves and service connections.
3. Water supply system
• Concerned with extraction, treatment and supply
• Water supply system includes
– Water pumping, storage and treatment
– Water transmission and distribution
• Water pumping is concerned with
– Lifting of water from source to storage
– Forcing water through water treatment facilities
– Forcing water through transmission and distribution systems
• Water storage could be
– at source prior to transmission
– at the treatment plant (before and/or after)
– in between the transmission and distribution systems
– within the water distribution system
• Water treatment could be
– limited just to disinfection
– conventional (suspended & colloidal solids removal, and disinfect)
– advanced (softening/demineralization, and removal of heavy
metals, flourides, organics, etc.)
4. Transmission System
• Conveys water from source(s) to a Distribution system, often
through a Water treatment plant and/or Storage Reservoir(s)
• Untreated and/or treated water is transmitted
• Gravity flow transmission lines, through shortest route
bypassing rough/difficult and inaccessible terrain are preferred
• Pumped/gravity flow pipelines, or gravity flow canal/
aqueducts, or gravity/pressure type underground tunnels
• Tunnels are opted when other alternatives are either not
available or not economical
• Gravity systems are low cost and no energy alternatives
• Pumped systems have high operation and maintenance costs
• Systems pumping to distribution systems often have provisions
to send excess water to storage reservoir(s)
5. Design of transmission system
• Transmission lines are designed to accommodate flow for the
Maximum Day Demand (MDD) of the design year
– Transmission systems directly connected to distribution systems
are designed for the Maximum Hourly Demand (MHD)
• The smallest diameter transmission line that can be provided
has the average water demand capacity
– Variable demand (including seasonal fluctuations) can be
accommodated in storage tanks, which are usually designed to
handle the daily fluctuations
– Transmission systems are usually designed for MDD + industrial
demand + fire flow capacity
– For systems, with storage reservoirs of 20-25% of average day
demand (ADD) storage capacity, the capacity is 1.3 times ADD
• While sizing the transmission lines, allowance is given to the
loss of carrying capacity due aging of the lines
• Flow velocity in the transmission lines should be <1.5 m/sec.
• Provide multiple conduits whenever possible (for reliability)
6. Transmission System
Pressure mains/ pipelines
• Less governed by route topography and routing can be along
the roads and public ways closely following the ground surface
• Hazen-Williams formula or Dorcy-Weisbach formula is used
• HGL must always (during maximum possible flow!) be
maintained above the pipeline (no negative pressure)
• Maximum pressure withstood by the pipeline must also be
taken into consideration – it should be < set value (70 m!)
– Occurs during flow shut-off conditions (in gravity systems!) –
(shutoff at source can tackle the high HGL problem!)
– Break pressure tanks (with open water surface), installed along
the main pipeline (and pressure reducing valves!) can limit the
maximum pressure/HGL
• Some minimum cover (>0.75 m!) is provided over the pipeline
– The cover must be > the frost penetration depth
– It must be sufficient to support the imposed dead and live loads
7. Transmission System
Channels/canals
– These are gravity flow systems (Manning formula for the design)
– Flow velocities are 0.3 to 0.6 m/sec. for unlined channels and
1.0 to 1.5 m/sec. for lined channels
– Recommended for raw water transmission (not treated water)
– Possible pollution of water from surrounding areas
– Water losses to percolation and evapo-transpiration and misuse
of water should be taken into account
– Trapezoidal sections are considered as the most economical -
Rectangular can prove economical when cut through rock
– Transmission lines must be avoided through the landslide prone
and flood prone areas
Gravity tunnels and aqueducts
– Laid below the HGL and designed for 3/4th full flow
– horseshoe shaped gravity tunnels are used (for structural
reasons)
– Manning formula is used
– Rock tunnels require thorough geological investigations at the
design stage
8. Appurtenances
Valves
• Devices used to control of movement of water and/or air
through pipelines by opening or closing to different extents
• Commonly used types of valves
– Block/isolation valves (allow full flow or no flow) - Shutoff valves
(at all reasonable locations to isolate pipeline sections for R&M)
– Control valves
– Directional (or check or non-return) valves
– Pressure reducing valves
– Altitude valves (and float valves!)
– Air valves (air release valves and vacuum breaking valves)
– Scour valves (blow off valves at each depression to drain the
pipeline) – 50 mm size per 300 mm diameter
• Smaller diameter bypass valves around larger diameter inline
valves (to equalize pressure across and facilitate valve opening)
9. Appurtenances
• Gauges and meters
• Break pressure tanks
• Devices like surge tanks (to dampen or eliminate water
hammer effects)
• Joints (Slip on and mechanical) to attach pipes together or to
attach pipes to other devices
• Unions and couplings: provided in pipelines (to join two same
dia. pipes) to facilitate repair – couplings are cheaper than
unions
• Reducers, elbows and reducing elbows, tees (for pipe size
reduction, for change of flow direction)
• Tees and crosses (for dividing flows)
• Caps, plugs and blind flanges (for stopping the flow)
• Thrust restraint designs
10. Air handling
• Air accumulates at the intermediate high points in the
transmission line - sources of air can be
– Flow start up
– Low flow
– Air super saturation
• Avoid negative HGL in the transmission system - negative
pressure prevents discharge of the accumulated air through
the air release valves
• Provide air release valves as required
– Air release valves must be located precisely
• For flexible pipes that might collapse under vacuum provide
vacuum release valves as necessary
• Provide vacuum release valves adjacent to the shutoff valves
on the upstream side
11. Appurtenances: Pressure
reducing valves
• These throttle automatically to prevent the
downstream hydraulic grade from
exceeding a set value
• During operation, the valve continuously
opens and closes to maintain a flow of
fluid at the reduced pressure
• The operation depends on balance
between fluid pressures acting above and
below a piston, and a spring force
• The piston is pushed down by the forces of
the low pressure fluid plus the spring, on
the other hand the piston is pushed up by
the force of the high pressure fluid
12. Materials and coating
Problems
• External and internal corrosion
– Corrosivity of the soil (in case of birried pipelines) and ambient
air (in case of exposed pipelines) and UV degradation
– Treated or untreated water and water quality, resistance to flow
and loss of pipeline capacity (hydraulic efficiency)
• Pipe erosion
– Flow velocity, sediment transport and scouring
• Pipeline strength
– Head/pressure and stresses (from water hammering!)
Solution to problems
• Pipeline material selection
• Internal and external coating
– Tuberculation, slime formation and encrustation can be controlled by
using specific materials and coating
– Materials and coating should take into account the structural strength,
field conditions, cost and maintenance requirements
• Positive corrosion protection (cathodic protection!)
13. Materials and coating
• Commonly used materials
– Cast iron, ductile iron and mild steel
– Pre-stressed concrete, reinforced cement concrete, asbestos
cement
– Polyvinyl chloride (PVC), Glass reinforced plastic (GRP), plastic
• Pipe material selected should withstand the highest possible
pressure in the pipeline
– Non-metallic pipes may be used only in non-freezing climates
– Iron and steel pipes subjected to freezing must be insulated or
protected
• Pipe material degradation by ultraviolet must be protected
14. Factors in Selecting Pipeline Materials
Flow Characteristics: friction head loss and flow capacity
Pipe Strength: working pressure and bursting pressure rating
should adequate to meet the operating conditions of the
system
Durability: sufficient life expectancy given the operating
conditions and the soil conditions of the system
Type of Soil: Select the type of pipe that suits the type of soil
• acidic soil can easily corrode G.I. pipes
• very rocky soil can damage plastic pipes unless properly bedded in
sand
Availability: Select locally manufactured/fabricated pipes
whenever available.
Cost of Pipes:
• Initial cost
• Installation cost which is affected by
• type of joints (screwed, solvent weld, slip joint, etc.)
• weight of pipe, depth of bury required, width of trench and depth of
cover required
16. Water distribution system
• Objective is distribute adequate quantity of water at adequate
pressure to individual consumers
– The treated water transmitted and/or stored is distributed
• Main elements of a water distribution systems
– Pipe network with necessary valves and other appurtenances
– Pumping stations and Storage facilities
– Service connections with valves and fittings (water meters!)
• Plumbing system with cross connection controls and with sanitary
protection and backflow prevention
– Fire hydrants (provided only on ≥150 mm size distribution lines)
• Layout of a distribution system is determined by
– Size and location of water demands
– Street patterns and topography
– Location of water treatment and storage facilities
• A service area can have more than one distribution systems
17. Categories:
• Branching systems
• Grid systems
• Combination of both
Grid systems:
• have water supply from
two or more directions
• Pipe network loops
with nodes and
links/pipes
• Preferred and more
reliable
Branching systems:
• have dead ends
• permit water supply
from only one direction
18. Water distribution system
Adequate quantity of water (including fire water) at all times
within the pressure limits is the requirement
• Not excessive (prove costly and increase leaks & consumption)
• Sufficient pressure for fire fighting
– Minimum pressure at the fire hydrants
• 276 kPa during normal flow conditions
• 207 kPa during maximum hourly demand
• 138 kPa while supplying the fire flow
– Maximum pressure allowed at the fire hydrants is 689 kPa
Minimum pressure allowed at the remotest point of the
distribution system is 3 m
• Maximum pressure tolerable or allowable is 70 m
A water distribution system is often divided into multiple pressure
level sub systems
– Pressure reducing valves may be used to protect specific locations
There can be a separate fire storage and pumping system
19. Design of the Distribution Pipe Network
• Designed to handle Peak Hour Demand (PHD) or Maximum
Day Demand (MDD) + fire demand (whichever is larger)
• Minimum Hourly Demand is 0.3 times of ADD
• Maximum Day Demand is 1.3 times of ADD
• Peak Hour Demand (PHD) is 3 times to ADD/24 for < 1,000
population and 2.5 times to ADD/24 for > 1,000 population
• Velocity at design flows should be 0.9 to 1.5 m/sec.
• Minimum pressure allowed at the remotest point of the
distribution system is 3 m
• maximum pressure allowed is 70 m
• Head loss allowed in the pipelines is a minimum of 0.50
m/1,000 m and a maximum of 10 m/1,000 m
• Minimum pipe diameter for fire fighting is 6 inch
• Reservoir Capacity: 25% of ADD
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21. Hardy-Cross method
1. Skeletonization of the water distribution system
– Construct water distribution network of nodes and links (multiple
loops)
– Find out and record lengths of the links/pipes
– Workout water extractions and additions for all the nodes
– Incorporate storage reservoirs and pumps also as parts of the
network
2. Label all the nodes and the pipes, arrange in loops, assume flow
rate and flow direction for each of the pipes through water
balancing at each of the nodes
– Assign positive or negative signs to indicate flow direction (clock-
wise direction a positive sign and anti-clock-wise direction a
negative sign)
3. For each of the pipes
a. Assume pipe diameter
(0.9 to 1.5 m/sec. velocity at MHD or MDD + fire demand flow)
b. Compute ‘K’ value
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23. Hardy-Cross method
4. Compute head loss and head loss/ flow rate for each of the
pipes and compute flow correction for each of the loops
5. If the flow correction is significant, make flow correction to
each of the pipes
– In case of shared pipes among the loops apply the correction
as below:
– Addition of flow correction can result in change in the sign of
the flow (or flow direction)
Repeat the steps 4 and 5 till the flow corrections for all the
loops become insignificant
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6. Find flow velocities in each of the pipes and check whether
they are within the acceptable range (0.9 to 1.5 m/sec.)
– If not, adjust diameters of all those pipes for increasing or
decreasing the flow velocities
If diameter of any of the pipes is changed, repeat the steps 3 to
5 till the flow velocities fall within the range
– (designed for max. hourly flow or MDD + fire demand –
whichever is larger)
7. Once flow velocities in all the pipes are within the range,
find pressure at each of the nodes
Identify the node with the minimum pressure and adjust
pressures at all the nodes to satisfy the minimum pressure
requirement (3.0 m WC is taken as the minimum)
8. Find the maximum pressure at all the nodes and check if any
where crossing the maximum pressure limit (done at 0.3
times ADD flow
25. 9.5 MLD
2.5 MLD 2.0 MLD
4.0 MLD3.0 MLD
6.5 MLD
7.0 MLD 5.5 MLD10.0 MLD
A B C
D E F
G H I
500 m 550 m
450 m 650 m
550 m 500 m
550 m 700 m 600 m
650 m 500 m 700 m
Water supply pipe network analysis
Pipe diameter
Flow rates in the pipes
Pressure at the nodes
26. Fire Hydrants
Fire Hydrants provide water (fire extinguishing agent)
Fire water system includes water storage (service reservoir), water
distribution system and Fire Hydrants
– Fire water should be made available from the gravity storage
facilities (pump failures and electrical outages are possible)
Fire water may be supplied together with municipal water or there
may be a separate fire water system
– Redundancy is designed into the water supply system for
supplying the fire water
Hydrants are normally provided at intervals of 100 m (but the distance
can be suitably increased or decreased)
– In case of high hazard category industries, spacing is just 30 m
– For moderate hazard, the spacing is about 45 m
Hydrants should be located at a distance ≥ 2 m from the building
– Can be upto 15 m for protecting hazardous storages/processes
– No portion of building should be > 45 m from external hydrant –
if this requirement is not met, internal hydrants are provided
27. Fire Hydrants
IS standards
– IS 13039: 1991 (Reaffirmed 2000) – External Hydrant Systems –
Provision and Maintenance – Code of Practice
– IS 909 (1992): Specification for Underground Fire Hydrant, Sluice
Valve Type
– IS 908 (1975): Specification for Fire Hydrant, Stand Post Type
Two types of fire hydrants: Stand post type conforming to IS 908: 1975
and underground sluice valve type conforming to IS 909: 1992
– Stand post type hydrants are preferred – but, if likely to cause
obstruction to traffic or if liable to be misused by public,
underground type are provided
– Industrial establishments use only the stand post type hydrants
Dry barrel type hydrants are used in regions freezing temperatues
Fire water supply to fire hydrants should be from more than one
directions and the supply lines should be ≥150 mm or 6” size
Essential hydrant accessories (hoses with couplings, branch pipe with
nozzle, etc.) are provided near the hydrant in a hydrant box)
28.
29. Fire Hydrants
• The hydrants may have 1/2/3 outlets each with a landing valve
• Hydrant outlets (of underground type) and valves should be located
as near to the ground level as possible
• Fire hydrants are painted in standard colours for protection and for
aesthetic reasons
• Loose, crushed rock or gravel should be placed around the hydrant
shoe for drainage purposes
• Should be visible, immediately recognizable and accessible (vehicle
access) and should have necessary clearance
• Acceptable pressures of fire water system are 65-85 PSI and
tolerable range of pressure is 50-120 PSI
– Pressure available at hydraulically most remote hydrant is ≥3.5
kg/cm2 for light and moderate hazards
– For high hazard areas, the minimum pressure available should be 5.25
kg/cm2 at the remote point
32. Water Meters
Essential to determine quantity of water produced by WTP and
quantity of water consumed by customers (needed for billing)
• Meters help in determining leaks and breaks in the
distribution system
• Meters make customer conscious and conserve water
Water meters are of two categories: main line meters and
customer meters
• Mainline meters (4 types)
• Venturi, Orifice, Velocity, and Pitot tube.
• Customer meters (3 types)
• positive displacement, compound, and fire line
33. Water Meters
Positive displacement meters
• Capable of measuring small flows with high accuracy
• Counts the number of times a chamber is filled and emptied
• These meters fail if there are sediments or loose scales in water
• These fail if there is relatively small % increase above rated flow
Current meters: Measure flow velocity through a known area
Compound meters:
• Combination of displacement meters and current meters
• At low flow rates, these work like displacement meters, and when
flow reaches predetermined value, these operate like current meters
• These are very accurate and not broken by large flows
The fire line meter: A special kind of compound meter.
34. Protecting Water Quality in Distribution System
• Many water supply systems, due to economic reasons, do not
have 24-hour daily water service
• Creates risk of infiltration of polluted water into the water lines
• to counter this risk, residual chlorine (0.3 mg/L) is maintained in
water distribution system.
• Water mains are adequate separated from potential sources
of contamination (sewers, storm sewers, septic tanks, etc.)
• Cross-connections are avoided and backflow or back
siphoning (from a private plumbing system) is prevented
• Cross connections: connections that join or link a potable water
source with a source of questionable/unsafe water
• Avoid the situations giving rise to negative pressures in the
distribution system.
• Install NRVs and promptly repair leaks
• Minimize dead-ends to avoid water stagnation water (prevent
sediment deposition and bacterial growth minimization)
• Cover reservoirs and make all vents and openings secured and
vermin-proof
36. Pumping system
• Pumps, pumping stations and booster pumping stations
• Pumps, piping and equipment
• Must be sized to accommodate peak hourly demand and maximum
day demand plus fire water demand
• Pumping capacity must be adequate to discharge the peak flow
even with the largest pump out of service
• Must be dependability and availability
• )Multiple pumps and
• Uninterrupted/Emergency power (dedicated standby generator or
portable generator)
• Power cost of pumping must be lower
• Pumps with variable speed drives can be used
• Can prove less efficient than constant speed pumps if provided
where not needed
37. Pumping system
• Metering of pumped water for knowing losses from leaks and other losses
• Monitoring the pump efficiency
• Meters indicating, totalizing and recording flows
• Controls on pump operation
• Turn on and turn off of pumps in response to signals of pressure in
pipeline or water level in the storage tanks
• pump alarm systems (for pump failure, seal failure, start failure and
generator start failure)
• Water hammer analysis
• Pumping stations for protecting pumps, piping and equipment from local
climate and weather conditions; security requirements; protection against
moisture and other conditions; stucture housing pump, piping and
equipment
• Ease of operation and degree of maintenance required
38. Pumping
• Five types of pumps are used in the water supply system
• Low lift pumps: used to pump water from source to WTP
• High service pumps: used to pump water from the WTP and
discharge into the distribution system under pressure
• Booster pumps: used to increase pressure
• Recirculation pumps: used in the WTP
• Well pumps: used to lift water from wells/tube wells
• Static head of a pump system may vary with the fluctuating
water levels in the suction tank and in the discharge tank
• Normal or rated discharge: discharge when the pump is
operating at its maximum efficiency
• A pump is usually operated at 50-85% efficiency
• Shut-off head: head at which the pump discharge is zero
39. Types of storage or reservoirs
Impoundment reservoirs, underground reservoirs, surface or
ground level reservoirs, break pressure tanks, stand pipes and
overhead service reservoirs (elevated storage)
Underground and surface or ground level reservoirs may be a buffer
between a) source and WTP or b) WTP and distribution system
Underground reservoirs
– Provided if proves economical or if the hydraulic gradient allows
– Can prove protection against freezing, and sabotage and
destruction
– Land above the underground reservoir can be utilized
– Pumping of water may be required
Surface or ground level reservoirs
– Hourly water demand variations may be dampened and WTP
will not be handling the peak demands
– Used as a water supply source to the distribution system –
water pumped to the distribution system
• If located at higher elevation, can serve as a service reservoir (an
economic advantage over the elevated service reservoirs)
40. Types of Storage or Reservoirs
Stand pipes:
– Tall cylindrical tanks with two storages, an upper useful storage
and a lower supporting storage
Elevated tanks:
– Provided within the water distribution system to supply peak
demands and to equalize system pressure
• Water is pumped into the reservoir during low demand hours, and drawn
out during the peak demand hours
• When pressure in the mains drop (from increased water demand),
water is automatically feed into them and pressure is maintained
– Provides storage for fire fighting and for meeting emergency
water demands (during power failure, and repair, maintenance!)
– Storage capacity is adequate to meet operational, fire and
emergency demands (with pumps out of service)
– In case of water supply from a high elevation impounded
reservoir, it can also function as a break pressure tank
– Altitude valves, pump/level controls (high and low level
switches) and alarms may be used with the elevation tanks
41. Elevated Service/Storage Reservoirs
Location
• Location depends on local conditions
• Strategically located for maximum benefits
• Determine the best storage reservoir location to ensure flow,
pressure and water quality
• Usually located near centers of heavy water demands
– Industrial and high value areas require more elevated storage
than the low value areas
• Located on the highest elevation available or near the center of the
distribution system
• Often located to one side of the service area
• Often located at the beginning of the distribution network
• A distribution system can include more than one service reservoirs
• In case of the reservoir on the opposite end of the network, excess
water flows to the reservoir
42.
43. Reservoir Storage Capacity
Design involves consideration of storage capacity and operating range
of water elevations, etc.
Storage capacity: the sum of balancing storage, breakdown or
emergency storage and fire storage
Balancing storage: equalizing the fluctuating demand against supply
– Equalizing storage mass curve of hourly rate of water consumption is
constructed for a MDD day
– 25% of the MDD is usually taken as the balancing storage required
Breakdown or emergency storage (failure of pumps, drives or electrical
outage)
– Usually expressed as percentage of Average Day Demand (25%)
Fire storage
– 1 to 4 liters per capita may be sufficient
– Supply of 2-12 hours of fire flows is considered sufficient (larger
communities require longer duration of fire water supply)
– 3785 LPM for 2 hours in the areas of no unusual hazards!
– 19000 LPM for 3 hours for commercial, industrial or urban-wild land
interface areas!
44. Elevated service/storage reservoirs
Operating range of water levels in the elevated
reservoir
• Maximum water level in the reservoir
– Minimum allowable pressure in the water distribution
network
– Head loss between the minimum allowable pressure
location and the reservoir location for the maximum
hourly flow condition of a maximum daily demand
• Minimum water level in the reservoir
– Minimum allowable pressure in the water distribution
network
– Head loss between the minimum allowable pressure
location and the reservoir location for the average
daily demand flow condition
45. If the Average Day Demand (ADD) is 1.0 then
– The Maximum Day Demand (MDD) is 1.3
– The Maximum Hourly Demand (MHD) is 2.5
Balancing Reservoirs are sized for hourly fluctuations
understanding of the variability in supply and demand is essential for sizing
the reservoirs
Functions of Service Reservoirs
• To equalize variation in hourly demand of water to a uniform rate of
supply from the source
• To maintain the desired minimum residual pressure in the distribution
system
• To provide the required contact time for the disinfectant added in order to
achieve effective disinfection
• To facilitate carrying out repairs on the pumping and transmission system
46. Types of Storage Reservoirs
• Balancing reservoirs and Service reservoirs
• Elevated/Overhead reservoirs/tanks or Ground level/Underground
reservoirs/sumps
Elevated reservoirs
– Provide the necessary pressure in the distribution system
– Desirable because of their reliability in meeting the short-duration high-demand rates
through gravity flow - maintain supply even in the event of pump breakdown
– Allow simple control of operation of pumps in filling the tanks
– Elevated Reservoirs are more expensive
Ground level reservoirs serve as suction sumps for pumps.
Service Reservoirs
• In case the supply is not continuous and it is only during certain duration
and the water distribution is intermittent for certain specified hours
different from the supply schedule, then the supply from the source is
stored in a storage reservoir and then supplied to the consumers
• This type of storage reservoir is called Service Reservoir (SR)
• The Service reservoir is provided with separate inlet and outlet
connections with control valves.
47. Balancing Reservoir
• When the supply from the source is continuous, the water
transmission main is connected directly to the distribution system and also
to the storage reservoirs
• During the lean demand periods, the excess supply from the source is
stored in the storage reservoir and during peak demand in the distribution
system, water from the source as well as from the storage reservoir will be
supplied
• The storage reservoir operating under this condition is called Balancing
Reservoir or floating reservoir
• Only one pipe is connected to the reservoir, which will act as inlet as well
as outlet
• In a water supply system with number of service reservoirs one for each
zone, they can be connected to a master balancing reservoir (MBR) so that
the proper distribution of water to each of the SRs can be achieved by
supplying through independent feeder mains.
48. Underground Reservoirs
• Underground reservoirs serve as suction sources for pumps. These are
normally built at the site of a supply source
• Water treatment plants also commonly have large reservoirs to hold
treated water
• Service pumps draw water from the reservoir and discharge into the
transmission and distribution system
• These can be either completely buried, partially buried or completely
above grade.
Storage Volume of Reservoirs
• The volume of water storage needed depends upon the following:
– Maximum rate of peak hourly demand,
– Maximum rate of pumping, and
– Duration and actual schedule of pumping and distribution in a day.
• Volume of storage in the reservoirs and rate of pumping are so fixed to
permit the pumping at average rate during the period of maximum
demand
49. • The maximum duration of pumping is usually limited to 20 hours in a day
• Two shifts of 8 hours each totaling 16 hours pumping is commonly
adopted
• The general norms for volume of storage required with reference to
duration of supply from the source
– Above 16 to 24 hours: 20 to 25%
– Above 12 to 16 hours: 33.33%
– Above 8 to 12 hours: 50%
– Less than 8 hours: 100%
• The day is divided into number of periods of different rate of demands.
• For each of the durations, the demand, the supply, cumulative demand,
cumulative supply and cumulative deficits are worked out
• The volume of water storage required is the absolute sum of the
maximum positive and negative cumulative deficits
• The urban water supply system could have all of its storage in elevated
tanks - but such practice may be very expensive – hence , provide a
portion of the required volume in the underground water storage
reservoir
50. Mains leading to and from the reservoir should be
large enough to handle max. emptying/filling rates
Control mechanisms should be there to keep the
tank as full as possible at all times
Level recording device at the reservoir can transmit
information to pumping station for pump regulation
51. Maintenance of Storage Reservoirs
• Proper maintenance of storage facilities is essential.
• All tanks should have tops or covers, and screens on air-vents
and overflows
• All tanks should have an exterior float gauge on the outside
• For good quality water, tanks must have complete turn-over
• Most tank floors slope toward a drain
– This drain should be valved
– It is best to lower the tank as low as possible prior to drain out
• All tanks should be drained, cleaned, inspected and
disinfected periodically
– Removal of any silt accumulated at the bottom of the tank
– Periodic inspection of the interiors of tanks
– Material and coatings used in the mains, tanks or reservoirs
should be corrosion resistant
• The materials and coatings causing taste and odor, color, turbidity
or toxicity must not be used
