Transmission losses for water

   My name is sitaram and i am an engineering graduate. It is out of interest that i am asking the following question. Recently in a discussion we had, i came across a point that " there are transmission losses in transmitting the water from one place to other: so my questions are :

1 What are transmission losses?
2 how they occur and what are methods that may be adopted to avoid them  ?

thanking you
sitaram akkaraju
(DONIMALAI- Karnataka)