Dairy industry expansion using open lot designs has impacted water quality and groundwater usage in parts of Central Texas. Field research was conducted at commercial dairy farms in Erath County, Texas, to develop improved design criteria for storage, treatment, and land application systems for open lot dairies. Water use and wastewater from milking parlors were monitored along with runoff from open lots. Water use for milk sanitation and manure removal averaged 148 L per cow per day. Two-stage anaerobic lagoon systems achieved higher solids and nutrient removal efficiencies than a combination of settling basin and one-stage anaerobic lagoons. The two-stage anaerobic lagoon system with 81- to 118-day hydraulic retention time reduced concentrations of volatile solids (VS), chemical oxygen demand (COD), and total kjeldahl nitrogen (TKN) in dairy wastewater from milking parlors by 80 to 82%, 90 to 93% and 55 to 73%, respectively. Solids settling basins reduced VS, COD, and TKN concentrations in wastewater by 35 to 45%, 27 to 47%, and 14 to 24%, respectively. As compared to second-stage lagoon effluent, open lot runoff was higher in K, but similar in TKN and P concentrations and contained a greater proportion of fixed solids. Analysis showed that anaerobic lagoon effluent and open lot runoff were good sources of available plant nutrients.