Sewage effluent for cooling has been utilized in the Texas Abstract: Saudi Aramco's Dhahran Utilities department is concerned about both biocide cost and biocide performance for the operation of its seventeen cooling towers (40 cells). The department tested alternative biocides and is now using an effective low cost biocide. Slug dosing calcium hypochlorite was used for many years for microbiological control on the cooling towers. The cost of the calcium hypochlorite was relatively low, however, when it was slugged dosed, the calcium hypochlorite oxidized expensive anti scalant, reducing heat exchanger protection. Therefore using calcium hypochlorite had a high overall cost. The department tested non oxidizing biocides to eliminate the anti scalant oxidizing problems. The non oxidizing biocides worked but they cost twenty times more than calcium hypochlorite. Also, the cooling tower operators did not like the safety concerns with non oxidizing biocides. The department successfully tested and is now using a low cost biocide that is normally used for swimming pools. Testing included microbiological test to confirm the biocides effectiveness. since the early 1060's. A history of cooling water treatment for electricity production, as well as recommendations for new installations will be presented.