An excel-based calculator (WatBal-Dairy) was created as a framework for water use accounting of dairy farm operations. The water use of alfalfa was measured in situ and compared to Denitrification and Decomposition (DNDC) model results in anticipation of using DNDC outputs in WatBal-Dairy. Results highlighted the need to calibrate DNDC to Canadian growing conditions with the model over-estimating measured evapotranspiration (ET) (34.1%), net ecosystem exchange of carbon dioxide (11.8%) and biomass (9.7%), while under-estimating soil moisture (-12%). The WatBal-Dairy prototype was created using validated empirical models for cattle and barn water use and tested using operational data including measured cattle intake and washwater from a working dairy farm near Ottawa. The study farm water footprint was 1025.7 kg H2O L-1 FPCM; precipitation (green water) accounted for 99.35% and pumped (blue) water 0.45% of inputs. Consumption was dominated (99.6%) by the field environment (crops and pasture).