In distillation why id the water fed in at the lower end of the condenser?

Here,it is because of simple law of gravity ,as the water flows from higher level to lower level due to its relatively higher density than the air . By connecting the cooling system from the lower end ,the water is flowing from lower level to higher level,Therefore, it will move slowly and full utilisation of cooling capacity of water can be achieved. If it flows from higher level to lower level it will flow due to gravity and the time taken will be lesser and hence ,partial utilisation of cooling capacity of water. To make the water move from lower level to higher level we have to supply some pressure difference or energy.