IEEEUnderwater wireless sensor networks (UWSNs) are utilized for a wide range of monitoring and surveillance applications. Lifetime maximization and maintenance of network reliability are among the most important considerations in the deployment of UWSNs. k-connectivity is a robust approach for reinforcing reliability. However, maintaining k disjoint paths from each sensor node to the BS, inevitably, results in extra energy dissipation, which reduces the network lifetime (NLT). Yet, there is no systematic exploration to determine the extent of lifetime reduction due to the increase in the k value, in the literature, to the best of our knowledge. In this study, we create an optimization framework to be able to explore the trade-off between NLT and k-connectivity based reliability in UWSNs. Through the optimal solutions of the proposed optimization model for a large set of salient parameters, we characterize the inter-play between lifetime and k-connectivity. Our analysis reveals that the k value to be maintained in a UWSN can affect the NLT significantly.