Water treatment is any process that improves the quality of water to make it appropriate for a specific end-use. The end use may be drinking, industrial water supply, irrigation, river flow maintenance, water recreation or many other uses, including being safely returned to the environment. Water treatment removes contaminants and undesirable components, or reduces their concentration so that the water becomes fit for its desired end-use. This treatment is crucial to human health and allows humans to benefit from both drinking and irrigation use.

1. WATER SUPPLY ENGINEERING
ENVIRONMENT ENGINEERING I
WATER DISTRIBUTION RESERVIORS

2. Storage of Water
Storage of Water may be required at several stages in a water supply systems.
Storage before the intake: Dam or impounding reservoir may be needed for tapping water streams
with low and inconsistent flow.
Storage after the intake, before the treatment plant: Reservoirs may be build to store water for
consistent supply to treatment plant
Storage after the treatment plant: Treated water must be adequately and safely stored before it
reaches the end consumer.
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4. Locating Storage Reservoirs
1. Located near the center of the service area, especially in flat areas.
2. Placed to alternate locations depending on the regional geography between the source and the
city.
3. In hilly areas, in order to harness the natural potential energy, it may be more advantageous to
built reservoir at the highest point even if it lie at one end of the area instead of the center.
4. When water is sourced from higher level reservoir, the service reservoir may function as a
pressure‐reducing device, reducing the possibility of damage to the pipes due to high hydrostatic
pressure.
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5. Types of Storage Reservoirs
I. Raw Water Storage Reservoir are used to store raw waters from the source before the
treatment plant for consistent supply of water.
II. Clear Water Reservoir are used to store treated water at WTP before pumping to distribution.
III. Distribution or Service Reservoirs store water at required head before distribution. These are
located close to ‘center of demand’ of the distribution network for optimum service.
IV. Intermediate Tanks or Balancing Reservoir may also be provided downstream of Distribution
Reservoirs (within the distribution network) for storing water during low demands and supply
during peak demands.
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6. Types of Storage Reservoirs
Based on the elevation with respect to the ground level:
Ground storage reservoirs (GSR) –
Below the ground – Underground reservoir
On the ground – Ground‐level reservoir
Elevated storage reservoir (ESR) –
In an elevation – Elevated reservoir
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7. Ground Storage vs Elevated Storage
GROUND STORAGE
1. Used when there convenient High ground
2. Ground storage is more economical
3. Used for large local supplies
4. No limit to the size of the reservoir
5. Requires less maintenance
ELEVATED STORAGE
1. Set up when there no convenient High
ground
2. Elevated storage is less economical
3. Can be used for supply with shorter
connection pipelines
4. Practical limit to the size of the reservoir
5. Needs more maintenance
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8. Reservoir Designing and Construction:
Surface Reservoirs
Surface Reservoirs
Typically circular, square or rectangular tanks.
Usually, shape of the land available is often
determining factor in built up areas.
A circular tank is geometrically the most
economic in shape (least amount of walling), but
needs flat ground.
Many times, rectangular tanks prove more
economical by making best use of available land.
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9. Reservoir Designing and Construction:
Surface Reservoirs
Surface Reservoirs
Two compartments - maintenance, this is very
difficult attain in circular shape.
The economic depths of the reservoir may be
determined considering the cost per unit area
i. 2.5‐3.5 m for reservoir capacity up to 3500
m3
ii. 3.5‐5 m for reservoir capacity ranging
between 3500‐15000 m3
iii. 5‐7 m for reservoirs of higher capacity.
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10. Elevated Storage Reservoirs or Elevated
Service Reservoirs (ESRs)
Constructed when sufficient high ground above
the distribution area is not available for the
construction of ground reservoirs.
Water level is maintained in these reservoirs to
obtain gravity flow for the distribution network at
adequate pressure at consumer taps.
R.C.C. or steel. Prestressed R.C.C. tanks are also
being used as they are economical than plain
R.C.C. tanks.
These are made in various shapes depending on
the designing engineers, such as circular,
rectangular, egg-shaped etc.
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11. Reservoir Designing and Construction:
Elevated Reservoirs
The ESRs need several accessories including Inlet, outlet,
overflow and drain pipes, water depth indicator, ladder,
manholes, ventilators.
Automated system to stop plumping when the tank is full
is also provided these days.
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12. Capacity of Storage Reservoirs
The minimum service or balancing capacity depends on:
◦ Hours and rates of pumping in a day
◦ Daily variations in the demand
◦ Hours of supply
◦ Type of network (loop or branched)
◦ Reliability of source
◦ Pumping capacity (standby pumps)
In case of continuous supply, reservoir capacity is usually about 25‐35% of quantity of water to be
supplied in a day, while larger storage capacity is needed for intermittent supply systems.
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13. Storage Zones in Reservoirs
Operating Storage/Useful or live storage: it
is the difference in volume between the “pump
on” and “pump off” levels when the tank is
normally being used and the sources of supply
pumps to the storage tank are off.
Equalizing Storage: This is used when the
source pumping capacity cannot meet the
periodic daily (or longer) peak demands.
This storage allows water production facilities to
operate at a relatively constant rate.
Daily peak rates compared to the average daily
demand determine the volume for this storage.
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14. Storage Zones in Reservoirs
Standby or Breakdown or Contingency
Storage: provide a measure of reliability should
sources fail or when unusual conditions impose
higher demands than anticipated.
Emergency or Fire Storage: This storage
takes care of the requirement of extinguishing
fire or other unusual emergencies.
Dead Storage: The bottom zone of storage in
a reservoir is known as dead storage. Water from
dead storage cannot be drawn out or used
beneficially because of piping elevations or low
pressures.
Effective Storage Volume = Total Volume ‐ Dead
Storage
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15. Recommended Readings
i. Mark J. Hammer; Water and Waste Water Technology; Prentice Hall of India.
ii. S. K. Garg; Water Supply Engineering; Khanna Publ.
iii. B. C. Punmia, A. K. Jain; Water Supply Engineering; Laxmi Publication.
iv. G. S. Birdie; Water Supply Engineering and Sanitary Engineering; Dhanpat Rai.
v. R. C. Rangwala; Water Supply Engineering, Charotar Publ. House.
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