Dissolved water in insulating liquid had been regarded as a kind of impurities that deteriorate electrical properties. Recently, the state and the behavior of water molecules in liquid were measured by IR method. And it had been analyzed where water molecules bond around dielectric molecule and how many molecules gather around polar base among the alkyl chain. The transformer oil consists of saturated hydrocarbons that are composed of the various length of alkyl chain. So in the case that hydrocarbon molecules include the polar base such as carbonyl group and ketonic group because of aging and oxidizing, it should be cared that water cluster interact with not only polar groups but also hydrophobic groups. In this paper, water was dissolved in ketonic compound with various length of alkyl chain. The effects of hydrophobic groups on the ratio of water clusters and on the conduction of water cluster were discussed. As a result, when the alkyl chain of ketonic compound become long, the ratio of small water clusters such as dimer and trimmer decreased. And the result from the relationship between the ratio of water clusters and the conductivity, it was appeared that the small water cluster contribute to increase of conductivity.