Because of the uncertainty of water resources in the western U.S., the Long Beach Water Department (LBWD) is considering seawater desalination as a possible source to augment its existing water supplies. An AwwaRF-funded project is examining dual-staged nanofiltration (NF2) for seawater desalination as an alternative to traditional reverse osmosis (RO) membrane treatment. The primary goal of this research is to determine whether this desalination system can reduce the operational cost for desalination, as compared to more traditional methods, by lowering operating pressures while producing potable water. A secondary objective was to evaluate the effects of blending desalinated seawater into LBWD's existing water supplies made up of treated groundwater (GW) and purchased surface water (SW). The existing finished water varies in composition during the year, with 100 percent of GW in summer, and 100 percent of SW in winter, the latter being provided either as State Project water (SPW) or Colorado River water (CRW). Based on these conditions, the objective is to determine the percentage of desalinated water (DW) that can be blended while considering the issues of DBP formation, disinfectant residual, and corrosivity. The paper presents water quality characteristics for the various waters to be blended. The characteristics for DW vary depending on the permeate salinity and pH targets. The two pHs considered represent one that is similar to the existing pH condition of the water in the distribution system (8.0), and one that is required if additional boron rejection is required (with an interstage pH adjustment to pH 9.8). Includes 4 references, tables, figures.