Vegetated buffers strips typically have limited ability to reduce delivery of dissolved phosphorus (DP) from agricultural fields to surface waters. A field study was conducted to evaluate the ability of buffer strips enhanced with drinking water treatment residuals (WTRs) to control runoff P losses from surface-applied biosolids characterized by high water-extractable P (4 g kg -1). Simulated rainfall (62.4 mm h-1) was applied to grassed plots (3 m x 10.7 m including a 2.67 m downslope buffer) surface-amended with biosolids at 102 kg P ha-1 until 30 min of runoff was collected. With buffer strips top-dressed with WTR (20 Mg ha-1), runoff total P (TP = 2.5 mg L-1) and total DP (TDP =1.9 mg L -1) were not statistically lower (α = 0.05) compared to plots with unamended grass buffers (TP = 2.7 mg L-1; TDP = 2.6 mg L -1). Although the applied WTR had excess capacity (Langmuir P maxima of 25 g P kg-1) to sorb all runoff P, kinetic experiments suggest that sheet flow travel time across the buffers (∼30 s) was insufficient for significant P reduction. Effective interception of dissolved P in runoff water by WTR-enhanced buffer strips requires rapid P sorption kinetics and hydrologic flow behavior ensuring sufficient runoff residence time and WTR contact in the buffer. Substantial phosphate-adsorbent contact opportunity may be more easily achieved by incorporating WTRs into P-enriched soils or blending WTRs with applied P sources. Copyright © 2008 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. All rights reserved.