The sparse network topology, coupled with the limited availability of reference nodes in Under Water Sensor Network (UWSN), significantly reduces the effectiveness of multilateration based schemes for location discovery. In this paper, we propose to explore Out-of-Range information to resolve location ambiguities of unknown nodes, which can not gain sufficient reference nodes information. The proposed scheme is based on the observation that, if a node, N1, is out of the transmission range of another node, N2, the distance between N1 and N2 must be larger than a given threshold value. This information, referred as "Outof-Range" can then be used to eliminate location ambiguities of some unknown nodes in UWSN. The simulation results show that the proposed scheme can significantly increase the number of resolved sensor nodes, compared with multi-lateration schemes, in particular when the network connectivity is low. The increase can be as big as 50% in some scenarios.