One of the most important problems of industrial water is hardness. Hard scaling, decreasing in heat transfer rate, increasing energy consumption and need to chemical cleaning, are factors that increasing the operating costs and environmental pollution. Water hardness refers to the presence of dissolved divalent ions in water, mainly of calcium Ca 2+ and magnesium Mg 2+ . In addition to heat loss in heat exchangers, hardness can cause problems in process waters due to scaling of boilers, agitated tanks, pumps, pipelines and other process equipment. Water softening is a key process for separation of hardness ions in many industries to make the water suitable for use in cooling towers or to prepare it for additional purification. Failure to deal with the water hardness can increase costs significantly because of reduced volumetric capacity, reduced metallurgical performance, increased downtime for mechanical de-scaling or corrosion and premature equipment failure. Lime Softening Process (LSP) is a voluminous process in the water utilities that consumes a considerable amount of chemicals (mostly lime) and produces a large volume of sludge. Its performance can affect on downstream purification processes such as sludge handling and demineralization units. Upsets in LSP can occur frequently and quickly and it may take days to render it fixed. Two major components of operating costs of a softening process are lime consumption and sludge disposal, both of them depend on performance monitoring. In this these, investigation has been done on the lime processes for softening. In this process, lime is used for hardness reduction. Performance control of this process is highly important for regulating lime dosage and optimum hardness of treated water which are directly affected on desirability of the process. Therefore, conventional method for control of lime softening, based on alkalinity, has been investigated in addition to checking modern method based on electrical conductivity. The current method for performance control of lime clarifier is based on measuring simple alkalinity (P) and total alkalinity (M) so that the amount of (2P-M) changes from 5 to 15 ppm as CaCO 3 . Pilot and full scale experimental results showed that performance control based on alkalinity is not always correct and reliable and it does not result in minimum hardness in treated water in addition to it consists of lengthy tests and using of expensive chemicals such as indicators and generation of chemical waste. Our tests showed that with lime addition to water, both total hardness and also Electrical Conductivity of softened water decrease to a minimum value due to precipitation of insoluble products but then increase gradually as a result of excess lime. In addition, the bench scale tests demonstrated clearly that minimum hardness in the LSP concurrent with minimum Electrical Conductivity Experimental results, also show that measuring of electrical conductivity can be used as a simple, non expensive and less sludge method for achieving minimum hardness in treated water without any chemical waste. Pilot and full scale experimental results revealed that the performance control based on electrical conductivity is highly accurate in detecting the optimum operating conditions in addition to simplicity and easy control without any chemical waste. Keywords: lime softening process, monitoring, chemical method, electrical conductivity technique