The cooling tower objects have inputs for water evaporation, drift and blow down. See example file CoolingTower:SingleSpeed:MultiCell. See the Engineering Reference for equations used to calculate water usage.
Near the end of the cooling tower inputs are these fields:
CoolingTower:SingleSpeed,
SaturatedExit, !- Evaporation Loss Mode
, !- Evaporation Loss Factor {percent/K}
0.0080, !- Drift Loss Percent {percent}
ConcentrationRatio, !- Blowdown Calculation Mode
3.0000, !- Blowdown Concentration Ratio
, !- Blowdown Makeup Water Usage Schedule Name
When you run the simulation you should see these report variables in the rdd file:
Output:Variable,*,Cooling Tower Make Up Water Volume Flow Rate,hourly; !- HVAC Average [m3/s]
Output:Variable,*,Cooling Tower Make Up Water Volume,hourly; !- HVAC Sum [m3]
Output:Variable,*,Cooling Tower Make Up Mains Water Volume,hourly; !- HVAC Sum [m3]
Output:Variable,*,Cooling Tower Water Evaporation Volume Flow Rate,hourly; !- HVAC Average [m3/s]
Output:Variable,*,Cooling Tower Water Evaporation Volume,hourly; !- HVAC Sum [m3]
Output:Variable,*,Cooling Tower Water Drift Volume Flow Rate,hourly; !- HVAC Average [m3/s]
Output:Variable,*,Cooling Tower Water Drift Volume,hourly; !- HVAC Sum [m3]
Output:Variable,*,Cooling Tower Water Blowdown Volume Flow Rate,hourly; !- HVAC Average [m3/s]
Output:Variable,*,Cooling Tower Water Blowdown Volume,hourly; !- HVAC Sum [m3]