Theory:

a) Housing and Slums
Due to the increase in population, there is a lack of adequate space for housing and a marked reduction in the quality of housing in the urban areas. With further increase in urbanisation, this problem may increase in the years to come—the rapid growth of urbanisation results in the development of slums.
b) Over Crowding
Due to poor ventilation and sanitation in over-crowded areas leads to an unhealthy environment in the urban areas. Congestion is also the cause of many diseases and riots.
c) Water supply, Drainage and Sanitation
With higher rates of population growth, all the infrastructures are chocking to meeting the requirements.
No city in the world has round a clock water supply. Similarly, the drainage situation is equally bad. The removal of garbage is a Herculian task for urban local bodies.
d) Transportation and Traffic
Despite planning for future needs, unforeseen growth in urbanisation leads to inadequacy in traffic and transport. The increasing number of two-wheelers and cars put more pressure on the available infrastructure, making the traffic problem worse. They also cause air pollution.
e) Pollution
Urban areas are the major polluters of the environment. Several cities discharge their entire sewage and industrial effluents untreated into the nearby water bodies like rivers, lakes etc. Factories and industries in and around the urban centres release smoke and toxic gases which pollutes the atmosphere.