Question

In towns and cities generally the bore wells have to be dug very deepto get water as compared to bore wells dug in villages

Answer 1

due to the concentration of population at a small place the level of groundwater decreaes in towns or cities more vigorously than villages. 
density of population is low in villages so the there is no need to dig so deep in villages as comparison to cities.
understand it like you have four chocolates and 12 people to be distributed and in towns chocolates are same but the number of people is 40.