Provision is required to be made for storage of water for the following reasons:
ï To provide against interruptions of the supply caused by repairs to mains, etc;
ï To reduce the maximum rate of demand on the mains
ï To tide over periods of intermittent supply; and
ï To maintain a storage for the firefighting requirement of the building
Water may be stored in OHT and/or UGT
â Reinforced Concrete, Brick Masonry, ferrocement, MS, SS, Plastic or Glass reinforced panels. Lead based paint or Lead lined tank shall NOT be used
Tanks to be provided with â Manholes made of corrosion resistant materials with locking arrangement, Ladders for tank depth more than 900 mm, Overflow pipe to act as warning pipe, Vent pipe for tanks larger than 5 KL capacity, Scour pipe, mosquito proof brass grating for overflow & vent pipe, slope in the top slab of tank
If storage capacity is more than 5 KL, it is advantageous to arrange it in a series of tank so interconnected that each tank can be isolated for cleaning and inspection without interfering with the supply of water. The outlet shall be at the end opposite the inlet
The outlet pipe shall be fixed 50 mm to 75 mm above the bottom of the tank and fitted with a strainer, preferably of brass
Underground storage tank â
ï Design of the tank shall be such as to provide for the draining of the tank when necessary and water shall not be allowed to collect around the tank.
ï Should NOT be located in low lying areas or near any public or private sewer, septic tank, leaching pool or soakage pit.
ï Overflow of the tank should be well above (preferably 600mm) the external surface level and terminate as a warning pipe with mosquito proof grating.
ï Prevention of back flow of local surface water in case of local flooding
ï Tank top slab to take load of fire tender movement where anticipated
ï No common wall between tank storing safe water and tank storing water from unsafe sources
OHT â Bottom of tank shall be placed clear off the terrace slab such that the elevation difference between the outlet pipe of the tank and the highest fixture at the top floor of the building is 2m.
The quantity of water to be stored shall be calculated taking into account the following factors:
ï Hours of supply at sufficiently high pressure to fill up the overhead storage tanks;
ï Frequency of replenishment of overhead tanks, during the 24 h;
ï Rate and regularity of supply; and
ï Consequences of exhausting storage particularly in case of public buildings like hospitals.
In case of intermittent water supply, the following guidelines should be adopted for calculation of capacity:
ï When the supply is from main OHT, the capacity of individual OHT may be taken as half a day demand.
ï In case of all the other buildings (apartments, hotels, hospitals, and commercial), the capacity of UGT and OHT may be taken as one and a half days and half a day demand.
ï Wherever raw water and treated water are stored in separate UGTs, the combined storage capacity shall be of one and a half days demand.
ï In case of sewage treatment plant, for treated water storage in respect of flushing, one day flushing demand shall be stored in UGT or treated effluent storage tank which is part of the plant, and half a day demand shall be stored in OHT
NOTE: Minimum requirements for calculation of capacity of these storage tanks are as follows:
a) In case only OHT is provided, it may be taken as 33.33 to 50 percent of one dayâs requirement;
b) In case only UGT is provided, it may be taken as 50 to 150 percent of one dayâs requirement; and
c) In case combined storage is provided, it may be taken as 66.6 percent UGT and 33.33 percent OHT of one dayâs requirement
Where the water supply distribution system is catering for separate potable water and flushing water supply, and where reclaimed or recycled treated water is being used within the building, it shall be considered as dual water supply system.
ï In such cases, storages for flushing/reclaimed/recycled water shall be separated proportionately.
ï Adequate measures and precautions shall be taken for physical segregation for sanitary purposes and to avoid cross-contamination in the distribution system and to prevent back contamination of water supply sources
When only one communication pipe is provided for water supply to a building, it is not necessary to have separate storage for flushing and sanitary purposes for health reasons.
ï In such cases, tapping of water may be done at two different levels (the lower tapping for flushing) so that a part of the water will be exclusively available for flushing purposes.
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