There are many reasons for dampness due to leakage from over head water tank on the roof. Some reasons are given below.

1.      The leakage in water pipe line.

2.      The leakage in the bottom slab of water tank from side wall joints.

3.      Over flow from the water tank if ball cock is not provided.

For the protection against dampness, the leakage can be repaired as follows.

·        All the joints of water pipe line should be checked and if there is any leakage in the pipe line, tight the loose joints and ensure that there should be no leakage in the pipe line.

·        If there is leakage in the bottom of water tank or side, the tank should be made empty of water and should be cleaned thoroughly by wire brush and old plaster on side joints should be scraped. After cleaning the tank, apply neat cement coat on the top of RCC slabs of water tank and the joints of RCC slab and wall should be made round with cement mortar 1:2 and let it dry for the setting of mortar. Care should be taken that no water should be filled in the tank till the mortar is green (properly hardened).

·        If ‘Ball Cock’ is not provided in the water tank, the over flow of water from the tank spreads on the roof and causes dampness. So ‘Ball cock’ must be provided in the water tank.

·        In some cases after fixing ‘Ball Cock’, the water starts leakage due to abnormal pressure in the pipe or the water supplied in the tank through electric motor and the water spreads over the roof and causes dampness. These problems can be avoided by providing over flow pipe from tank to rainy water pipe. If the water comes in the tank more than its capacity, it will be automatically drain out through over flow pipe and will come to the ground through rainy water pipe. This way the dampness can be avoided.

If you are constructing a new over head water tank, follow the specifications to avoid any dampness from over head water tank on roof.

·        Keep the water tank 2 to 3 feet high from tile tracing of the roof for easy repair and cleaning in future.

·         Keep the ratio, 1:1.5:3 in cement concrete lain in RCC slab from the bottom of the tank and vibrate the cement concrete properly.

·        Finish the top of slab with water proofing compound and cement slurry while laying the slabs.

·        Plaster the bottom of the slab after removing the shuttering.

·        Fix all the water supply pipes during masonry work.

·         Plaster internal and external surface of the water tank with coarse sand in cement mortar 1:3 rendered in cement slurry.

·        Finish all the joints properly and round.

·        Fix proper overflow pipe which discharges into the rainy water pipe directly.

·        Fix ball cock with the water tank.

·        Fit all other joints of water supply pipes tightly.

NOTE:  If you want to construct insulated tank, follow the steps given below.

·         Make the bottom slab of water tank, 6 to 8 inches wide on all four sides.

·         Construct the external wall leaving the gap, 2 to 4 inches between the two walls after finishing the internal of the tank with plaster on both sides.

·        Finish the external wall with cement plaster all around.

·        Fill in the gap between the two walls with insulated materials.

·        Cover the top of water tank with insulated material.

·        Cover all the water supply pipes on the roof either with insulated material or kept in PVC pipes.