Book excerpt: Global water resources face a number of challenges. Growing global population and rising standards of living have led to increased water demand for domestic use, agricultural irrigation, and industrial processes. The effects of climate change have resulted in changes to historical patterns of rainfall and water supply. Severe and lasting water shortages are becoming more common and widespread, so that existing water infrastructure cannot provide stable resources in some regions. Alternative water sources, such as seawater desalination, brackish water desalination, and zero liquid discharge desalination, can help bridge this gap. However, to avoid amplifying the climate crisis, carbon emissions associated with desalination and brine concentration must be minimized. As a result of the rising use of desalinated water and the inherently large energy cost associated with desalinating seawater, developing efficient desalination technologies has become a major focus of water research. This work develops improved metrics, technoeconomic models, and technological advances to raise the efficiency and cost-effectiveness of desalination and brine concentration technologies. First, evaluating technological improvements and new technologies relies on the ability to fairly and accurately quantify the value of said improvements. However, accurately evaluating and comparing the energy consumption of desalination plants that use different forms and grades of energy is difficult. To fully capture the thermodynamic and economic cost of energy, and to fairly compare desalination systems that use different grades of input energy, energy consumption must be compared not at the point where energy enters the desalination plant itself, but as primary energy entering a power plant in a coproduction arrangement. The first section of this work investigates a variety of metrics for comparing the energy and exergy consumption attributable to desalination in coproduction plants, evaluates 48 different power-water coproduction systems, and compares the primary energy consumption of multi-effect distillation (MED) and reverse osmosis (RO) from a thermoeconomic perspective. The entropy generation at the RO membrane and in the MED effects are derived in similar terms, which enables a comparison of the overall heat transfer coefficient in an MED system to the permeability of an RO membrane. RO is shown to outperform MED in energy efficiency because of a balance of material costs, transport coefficients, and cost of energy. Second, technoeconomic principles from the first section are applied to a case study. This work evaluates the technoecnomic feasibility of collocating a seawater reverse osmosis desalination plant with an existing nuclear power plant, specifically the 2.2~GW[subscript e] Diablo Canyon Nuclear Power Plant on California's central coast. This work shows that at a collocated plant, the sharing of seawater intake and outfall structures, reduced power costs due to reductions in transmission costs, and potential additional cost savings from economies of scale could enable desalination plants to produce water at half the cost of other stand-alone desalination alternatives. This work is the first to show that collocated RO and nuclear power have strong coupling that results in a significant economic advantage over seawater desalination at other sites. These advantages are not unique to the Diablo Canyon site and should be applicable to dozens of existing nuclear power facilities. Third, this work evaluates newly developed brine concentration technologies, specifically low-salt-rejection reverse osmosis (LSRRO) and osmotically assisted reverse osmosis (OARO). A variety of technology configurations, including single and multi-staged systems are investigated and optimized. Systems are separately designed for both minimal energy consumption and minimum system size, resulting in a design envelope that contains all cost-optimal designs. This work improves on existing literature by simulating designs in realistic form factors and using probably membrane parameters. Evaluation of exergy destruction provides insight into system operation and optimization. This work shows that the novel semi-split OARO configuration improves on both split-feed and split-brine OARO configurations, improving both energy consumption and membrane usage compared to existing designs, and extending the operating range of standalone systems. LSRRO systems are likely to have smaller system sizes than OARO systems, although specific membrane costs will determine whether this translates to cost benefits.