The study aims to provide a framework for the quantitative evaluation of the water resources on a regional basis. The work involves hydrologic data augmentation and analysis of the water budget of the Central Luzon Basin, a humid, tropical region. Four hydrologic data augmentation methodologies -- percent deviation, HEC-4, YOR, and Matalas-Jacobs -- were analyzed and compared. Streamflow data of five gaging stations in the Central Luzon Basin were divided into early-half and late-half series. Augmentation estimates based on the late-half series were compared with the corresponding historical early-half series. The methods were assessed based on eight comparison items and two scoring systems. The comparison items considered were double mass analysis, mean, cumulative annual deviations, and standard deviations, for the annual flows; and maximum, minimum, mean, and standard deviations, for the monthly flows. The percent deviation method excelled in both scoring systems and was selected as the best method for the hydrological characteristics and type of available data in the region. Application of the percent deviation method in augmenting the record of selected streamflow gaging stations within the Central Luzon Basin pointed out some limitations of the method. These limitations may be remedied by proper selection of the station on which the augmentation estimates are based. Strong statistical relationship between the dependent and base stations, in addition to other hydrological factors, should be satisfied for the derivation of more reliable estimates in the application of the percent deviation to streamflow data augmentation. The water budget analysis revealed that about 54 percent of the annual precipitation in the basin is measured as streamflow. The balance of 46 percent is shared by evapotranspiration and change in basin storage. An average annual evapotranspiration of about 1,070 mm was found. This is about 0.5 of the average Class A pan evaporation data from two measurement points. Surface water resources remain the most important source of water for the basin requirements. No serious water quality problems exist and surface water in the basin is suitable for both domestic and agricultural purposes. Groundwater could be a promising alternative resource for both domestic and agricultural uses. High recharge during the rainy season, about 5,000 to 7,000 MCM, and relatively shallow aquifers are among the significant features of the groundwater basin.