High Voltage (HV) power cables need to be connected to other HV equipment such as transformers or overhead lines. To safely connect the cable to such equipments a cable termination is used. The cable termination is usually filled with a type of dielectric fluid and is fitted and sealed at the customer site. However during the installation of the cable termination man made errors can occur and in some cases, it can result in ineffective sealing of the termination. These may act as points from where moisture or water droplets can enter inside the termination. The moisture which enters into the insulating oil would move towards the regions in the termination where there is high electrical stress due to the dipole nature of the water molecule. This area of high electrical stress is usually the surface of the stress cone. Depending on factors such as the amount of moisture entering the termination, it could take months or a few years to effect the functionality and eventual failure of the cable termination. The preliminary failure investigation shows evidence that the failure is caused to the stress cone, which is usually in contact with the mixture of water and the oil. The electrical activity on the surface of the stress cone due to the combined effect of the oil and water causes some discolouration and tracking of the rubber material. There are two main tests that are conducted in this research, one of the test is focused on the oxidation process of silicon rubber by thermal stress. The second test is a small scale test setup with oil and silicon rubber electrically stressed in presence of water to understand the long term effect on the surface of the material. Both the experiments conducted produced partial results which could be used to explain the degradation of silicon rubber, also information of partial discharge patterns which could be useful in detecting such moisture induced faults in terminations.