How Do You Build an Overhead Masonry Water Tank? [PDF]

How Do You Build an Overhead Masonry Water Tank? [PDF] 

The terrace water storage tank is typically built with brick masonry and placed on an elevated platform to provide a reserve supply of water for daily house activities. The use of brick masonry in the construction of a water storage tank is a low-cost option for storing water.

In this article, we will go over the important specifications for building a masonry water storage tank on a terrace:

Location of Tank

The location of the water storage tank must adhere to the specifications listed below-

1. It must be close to the connections or fittings where the water is supplied in order to avoid long horizontal lengths of delivery pipe.
2. It should be as hidden as possible from the main road and the building's compound.
3. If the tank fails, the overflow pipe must discharge at a convenient and visible location so that it does not cause damage to the building.
4. A bottom clearance of at least 30 cm is required to allow for easy clearance of the terrace beneath the tank.

Size of the Tank

The tank's size is determined by the amount of water that must be stored. If the requirement is greater and more than one tank is to be provided at the same location, a larger tank of combined net capacity with suitable internal partitions may be built to achieve an economical design.

The suggested tank sizes based on water capacity, with a freeboard of 15 cm, are shown in Table 1 below-

Table 1: Size of the tank with respective water storage capacity.

Net Capacity(Liters)	Internal size (L X B X h)(cm)
300 liters	70 x 70 x 75
600 liters	90 x 90 x 90
900 liters	105 x 105 x 90
1200 liters	120 x 120 x 100
1400 liters	120 x 120 x 115
1600 liters	120 x 120 x 120
1800 liters	130 x 130 x 125

Construction of Overhead Masonry Water Tank on Terrace

1. Bottom Slab Construction

1. The tank's bottom slab shall be made of reinforced cement concrete in the ratio of 1:1:5:3. (1 cement: 1:5 coarse sand : 3 stone aggregate 20 mm nominal size).
2. The bottom slab must be supported structurally by brick masonry walls, reinforced cement concrete beams, or rolled steel sections, and must have a mild slope towards the scour pipe outlet.
3. For the sizes listed in table 1, the bottom slab thickness shall be 10 cm, and the reinforcement details for the slab shall be as shown in figure 2.
4. The structural engineer must supply the structural details for sizes other than those listed above, or for a combination of tanks.
5. If the slab is supported by brick masonry walls, the tops of the walls must be plastered.
6. If the slab is supported by an RCC beam, this can be integral or simply supported depending on the circumstances.
7. It is preferable to have a slab with simply supported conditions on the beam. If it is to be simply supported, the beam top should be rendered with neat cement and given a thick coat of limewash.

2. Construction of Tank Walls

1. The tanks' walls must be built with class 7.5N bricks and cement mortar 1:3 (1 cement: 3 coarse sand).
2. The first course of brick masonry should be laid immediately after concreting the base slab, i.e., while the concrete is still green, to form a good bond and avoid leaks or cracks.
3. The remaining masonry must be raised and completed within a week of the slab being laid.

3. Installation of Tank Fittings

The fittings recommended for the masonry water storage tank must be galvanized iron (GI), and this is assumed in the specification below.

A. Scour Pipe

To prevent slipping, a 40 mm dia pipe is joined with a 40 mm 'T' pipe, which will be embedded inside the wall to serve as a scour pipe. As shown in Figure 2, the end of this scour pipe must be equipped with a socket and plug (Detail A).

B. Delivery Pipe

The delivery pipe must be 20 mm in diameter and fixed at least 30 mm above the bottom slab of the tank to prevent silt from entering the pipeline and choking it, as shown in figure 2. (Detail B).

C. Overflow Pipe

The overflow pipe shall be 25 mm in diameter, with a socket at the internal end, and shall be fixed at the tank's freeboard level at a convenient point to drain out the overflow. The pipe, including the socket, must be 30 cm long.

D. Inlet Pipe

The inlet pipe shall be 20 mm in diameter, with a 20 mm socket at the internal end and, if necessary, a socket or elbow at the outer end, which shall be fixed at the freeboard level, as shown in figure 2. (Detail C).

E. Mosquito Proof Coupling

The inlet pipe must be 20 mm in diameter, with a 20 mm socket at the internal end and, if necessary, a socket or elbow at the outer end, both of which must be fixed at the freeboard level, as illustrated in figure 2. (Detail C).

F. Ball Valve

The ball valve must be made of brass and have a plastic float with a specified size and pressure. The ball valve must be securely attached to the tank in continuation of the inlet pipe and adjusted to limit the level of water in the tank at 25 mm below the overflow pipe lip.

4. Plastering of Tank

1. The base slab and sidewalls must be plastered from the inside with 1:3 cement mortar 15 mm thick (1 cement : 3 fine sand).
2. Plastering must be completed within one week of the side walls being constructed.
3. The interior junctions of the wall and the base slab, as well as those between walls, must be rounded with mortar 1:3 to reduce water pressure on the junctions.
4. All inlet, delivery, scour, and overflow pipe joints must be completely leak proof.
5. On the inner side of the tank, a coat of neat cement punning should be applied to the plaster on the surface of the walls and the base slab.
6. The same procedure must be followed at the top of the tank to serve as bearing plaster for the top side.
7. The tank's external walls must be plastered with 12 mm thick cement mortar (1:4). (1 cement: 4 fine sand).

4. Curing of RCC and Brickwork

1. The curing of RCC, brickwork, and plastering must follow general curing specifications.
2. The tank must be filled to half capacity on the first day and to full capacity the following day.
3. To prevent cracks in concrete from forming due to shrinkage, the water in the tank must be kept until the tank is used.

5. Construction of Top Slab

1. The top slab shall be 5 cm thick and made of precast reinforced cement concrete in a 1:2:4 mix.
2. The reinforcement details must be as shown in figure 2.
3. The top slab must be large enough to project 15 mm beyond the tank wall's external finished faces on all sides.
4. While casting, the top of the slab must be smoothed.
5. The frame of the C. I. hinged cover must be fixed beforehand so that it is embedded in concrete while casting the top slab.

6. Testing of Tank

1. The tank's water tightness must be tested at full supply level.
2. The test requirement is satisfied if the external faces show no sign of leakage and remain dry throughout the seven-day observation period, after allowing seven days for absorption after filling.

FAQs

1. What is the advantage of Masonry tank over PVC tank?

Because of the insulation value of concrete, masonry tanks are generally strong and long-lasting.

2. What is the cost per m³ for the construction of Water Tank?

The cost of the masonry tank will vary by country based on the cost of materials and labor. The probable cost per m3 for various countries is listed below-

1. $20 per m3 in the United States

2. Kenya - $37/m3

3. Sri Lanka - $28 per cubic meter

3. What size of tank should be used to store 1200 liters of water?

The tank sizes for various storage capacities are listed below-

4. What is the specification of Brick masonry used in the Water tank?

The tanks' walls must be built with brick masonry in cement mortar 1:3 (1 cement: 3 coarse sand) of class 7.5N bricks.