How can we reduce water loss? What are the major heads of water loss?

I hope I understand the question correctly.

I used to work in utilities sector.  From utilities provider point of view, water loss is mainly due to leaks in the distribution system.  In order to reduce it, regular leak detection should be carried out -use suitable equipment.  Also, there should be meters in the distribution system such that we can segregate the system into smaller sub-systems, so at least we can get an idea in which sector(s) the leakages are.  These meters should be checked more frequently than the monthly customer-meters reading.  Lastly, you should have quick repair.

I agree with Donno Maharanto answer

Major head loss in water supply pipelines are due to friction in pipes and minor losses are due to components such as valves, bends, tee joints 

 Limit and control the competing demands for fresh water, which led to the aggravation of the crisis as well as mismanagement, especially if we know that the latest studies published suggest that the missing of fresh water, especially in the Middle East than the size of the Dead Sea