Problems associated with rapid urbanization.
Access to water and electricity - Not all newcomers can get access to basic services. Not all parts of the city will have running water, sanitation electricity etc. 
housing - when people arrive at cities (from rural areas), there is often nowhere for them to live, especially since several of them are looking for cheap housing. Even for people with money, demand for housing exceeds supply. Most newcomers live in shanty areas. 
Traffic congestion and Transport 
As the city increases in size people have further to commute to get to work
pollution 
Public services
crime 
education - Rapid population growth = lack of schools. Also, schools are very expensive and some children need to help their parents. 
Social problems - Crowded and unpleasant environment causes crime. In some poorer areas, street gangs (involved in drug trafficking) lurk
Environmental issues
healthcare 
water supply can spread water borne diseases to a large amount of the population.
air pollution can cause asthma or allergies
second hand smoke can cause cancer
unemployment - Many people who move to cities still struggle to find proper paid work (as the workers are mostly farmers). Instead, they are either unemployed or work in the informal sector. Even when there is unskilled paid work, it is normally far away from the areas where newcomers live.
informal sector
uneducated people may be able to find emplyment
greenhouse gases
from vehicles 
from industrial facilities 
People move further from the city center to find cheaper housing. As a result they have to travel further
lack of access to public healthcare facilities.
people die or are injured by falling off of trains
lots of waste is created. only small amount is processed/treated properly, the rest gets dumped in landfills or rivers.
people turn to crime to survive
people in informal sector don't pay taxes to the government
people have to wait a long time at hospitals to get treated.
government doesn't have enough money to improve and provide more public service
Lack of trained professionals due to the low salaries