First we will  fill full  water in 4 liters  bucket and then pour it in 9 liters bucket . Then  we will fill half 4 liters bucket and then pour it in 9 liters bucket.
There is no mark in the bowl so how exactly u would measure half water in 4litre bowl?
First of all fill 9 litre bowl full.....then pour water from it in 4 litre then empty 4 litre again put the remaining water in the 9litre bowl  then empty it now again pour the remaining 1 litre of water in 4litre of bowl but this time keep it dont throw that.....then again fill 9 litre upto top now pour water from 9 litre to 4 litre bowl which has already 1litre now it will occupie only 3litre more and the water left in 9 litre bowl is 6litre