Principle
for the preparation of Water supply Scheme
1. Selection
of source:- Where raw water from flowing streams, lakes , tanks ad other
impoundment from contaminated catchments and ponds form the source, provision
should be made in the scheme for filtering such water prior to disinfection.
2. Quality
of water.- The chemical quality of supplies proposed from ground water through
tube wells, wells and infiltration works should be of acceptable quality, to be
adjudged wit reference to local condition, where special treatment of removal
of dissolved substance like iron, sulphates and flurides is necessary,
provision should be made there in the scheme.
3. Disinfections.
- It is
advisable to provide for continuous effective disinfections of supplies drawn
through tube wells, wells and infiltration works where local conditions
indicate the need.
Where surface water is the source, treatment
including filtration and disinfection of the final effluent is essential.
It is equally important to ensure that the free
residual chlorine of a minimum of 0.2 ppm is maintained at all points in the
distribution system.
4. Simple
drip-feed device.- For simple rural well supplies, disinfection should be
arranged by a simple and economical drip feed of a decanted bleaching powder
solution, the dosage being adjusted to suit the rate of draw from the source. A
simple gravity feed arrangement for such a purpose should be followed.
5. Pressure-feed
chlorinators. - There are different types of pressure-feed
chlorinators available for injecting chlorine solution into force mains. The
two good classification of these chlorinates are -
(a) the positive-feed type, and
(b) the vaccum type
The details of their working and operation, and
the care of chlorinator equipment are set out in paras 10-6-22 and 10-6-3 on
pages 132-136 of the Manual of Water supply issued by the Ministry of Health.
Common
defects and handicaps experienced in operating some of the pressure-type
chlorinators in the market are to be attributed to the provision of inferior
rubber holders, mal-adjustments of the plunger stroke and inferior types of
rubber diaphragm. Every care should be exercised in selecting a good and robust
quality of chlorinator suited to the needs of each case.
6. Structure
of infiltration galleries - In developing safe supplies through infiltration
works the essential details to be followed in the design of infiltration
galleries have been set out in the Water supply Manual .
7. Slow sand
filter.- Where slow sand filtration is adopted for treatment of raw water, the
design criteria to the adopted are as set out in the Water Supply Manual. A
typical design calculation to determine the economical size of filters is given
in the following page.
8. Type
design of iron removal plant. - A typical design of an
iron -removal
plant should b followed. The basic factors governing the design of such plants
are set out in the Water Supply
Manual. These may be adopted with suitable notification where
removal of iron from ground or surface water is necessary.
9. Mechanical fitter plants. - Where
full-scale treatment of raw water comprising chemical design mixing,
flocculation, sedimentation and filtration followed by disinfection is
necessary, the functional aspect of each component as well as the design criteria
recommended in respect of each, as set out in the Water Supply Manual may be
adopted with suitable modification.
10. Economical size for source mains. - the per
capita rate of supply to be adopted in respect of each community, the most
economical means of conveyance of the supply from the source to the service
points and the design of the distribution system in each case may generally
follow the guide - lines set out in the Water
Supply Manual.
11. Charts for pipe flow computation. - It is
recommended that Hazen and William's Formula
should be adopted in the design of pressure mains while the Cutter's Formula
orthe Manning's Formula should be used for free-flow
conduits. Readymade charts for computing pipe size under the Hazen and William
and Kutter's Formulae may be used.
The Hazen
and Williams's Chart is based on a value of 100 for 'c'. For
other values of 'c' applicable
to different pipe materials (as recommended in the Water Supply Manual) the
corresponding
figures will have to be deducted.
The
Kutter's Charts are for a value of 'n' =.015 which may be adopted for all pipes
upto 24 ‚dia. and masonry conduits of all sizes. A value of 'n' = .013 may be used for pipes
above 24? dia.
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