Neretva
Situated between the major regional rivers ( Drina river on the east , Una river on the west and the Sava river ) the Neretva basin contains the most significant source of drinking water . 
<triplet> Drina <subj> river <obj> instance of <triplet> Una <subj> river <obj> instance of <subj> Sava <obj> mouth of the watercourse <triplet> Sava <subj> river <obj> instance of <triplet> Neretva <subj> river <obj> instance of