A case study was conducted to evaluate and identify the main materials and sources affecting the conductivity of reclaimed industrial wastewater for reuse. There were two suppliers (food production companies, S and M) and two users (pulp and paper making companies, P1 and P2). The user requirements for quality of the reclaimed water were conductivity < $1,000{mu}S/cm$ and Volatile Suspended Solids (VSS) <10 mg/L. Conductivity of treated wastewater at M company varied from 872 to $1620{mu}S/cm$, but the VSS was very stable over the year, with an average of 5 mg/L. According to the source tracking of M company, it was determined that the main materials affecting conductivity were TDS, $Ca^{2+}$, and $Na^+$. Electrical Conductivity (EC) measurement is sometimes the only practical method for the analysis of Total Dissolved Solids (TDS); therefore, developing this relationship would be helpful for company-to-company wastewater reuse. In this case study, the ratio of TDS to EC was in the range of 0.58-0.67, with a mean value of 0.64 and a very strong relationship at the effluent point. Even though the results were from only one industry, this conversion factor could be used to estimate TDS using EC measurements for similar industrial wastewater and could motivate further research for the direct use of treated industrial wastewater. This study is a first case study of company-to-company wastewater reuse.