Moisture ingress in fibre optic cables affects performance by causing material instability, swelling and long-term degradation of the cable jacket. The Threat of Humidity and Moisture Humidity. Well, the short answer is yes – fiber optic cables can get wet to some extent without issues. But you do have to be careful, as too much water exposure can cause major problems over time. In this article, I'll go over everything you need to know about water and fiber cables – are they waterproof. Moisture causes reliability issues in fiber installations. Small jacket cuts, loose seals, or aging conduit allow moisture to enter.