Here we see that the water-usibg operation consistsof a water makeup(inlet) and water bloedown (outlet) The mass load of contaminante transferred to the water stream represents the increase in contaminant concentration in the unit due to evaporation the limiting inlet and outlet concentrations of the water stream are represented by the outlet and inlet concentrations respectively of the process stream the actual contaminant concentration at the inlet and outlet of the water-using unit must be less than these limiting concentrations