Question: what are the merits and demerits of water transport?
Answer: Less Maintenance Cost: Maintenance cost in rail and road transport is quite high but maintenance cost of water transport is quite less.
Cheap: ... 
Useful for Bulky Goods: ... 
Useful During Natural Calamities: ... 
Helpful in Defence: ... 
Important for Foreign Trade: ... 
Slow Speed: ... 
More Risky: