The building is almost 12 years old. We didn't have this problem before. But in this last 2-3 days some residents complained they have experienced shock coming form the pipeline of bathroom even after they shut down all the switches of MCB. I asked electrician he said the earthing of the building is damaged or degraded etc and needs to be changed.
Yes and is actually very common
One possible scenario is the service entrance cable.
Service cables installed correctly are supposed to have a drip line. This keeps rain from running into the sheath where it can stagnant and cause corrosion to the aluminum bare ground.
In homes with SEU wire, the bare ground serves as the neutral. When this is damaged, the electrical system, due to incorrect wiring, will erroneously use the grounding system to complete the path back to the transformer, and any metal/aluminum ducts, copper pipes, stainless steel appliances attached to the grounding system may have potential voltages. Unfortunately, a damaged service entrance wire is not easy to diagnosis. The obvious symptoms are usually dimming/brighter lights, dryer not drying clothes and other large appliances not working, and small electronics usually will be damaged.
The most likely scenario is a live wire is accidentally touching a part of the grounding system creating a trickle of voltage that lingers on until you notice it by getting zapped. The electrician should be able to isolate the suspected branch circuit and by running a new line, can remedy the problem.
Earthing can be damaged.
Whole earthing installation needs to be continuosly led to the ground, if something (a tree branch) or someone (a worker fixing house's external surface) brake the line, it needs to be checked and fixed. My parents' house have had a similiar problem some years ago. They were making additional thermal insulation on external surfaces and, after deteatching wire leading to ground rod. Fixing the continuity fixed the problem.
My first guess here is to check the connection to ground rods. I don't think that it can be 'degraded', 12 years are not that much, I guess.