A field study was conducted in Central Oahu on the effects of irrigation with recycled water on the receiving groundwater. The overall objective of this study was to evaluate the percolate water quality differences between irrigation with recycled water and the local groundwater, which is the current source of irrigation water. A significant difference in the percolate water quality could indicate a potential cause of concern. No significant difference would indicate that there is no cause for concern when irrigating with recycled water. The results from the percolate water were used to model the impacts on groundwater quality.