What effect does water have on the glass core of an optical fiber?

Water can indeed have a detrimental effect on the glass core of an optical fiber, leading to increased attenuation of the light signal within the fiber. When water infiltrates the fiber, it can create a situation where the core's refractive properties are altered. This alteration can result in scattering and absorption of light, which diminishes the clarity and quality of the transmitted optical signal. Therefore, the presence of water makes the glass core less effective at transmitting signals, making it essentially opaque to the light signals that the optical fiber is designed to carry.

In contrast, the other options suggest positive effects, which do not apply to the interaction between water and the glass core. Water does not enhance signal clarity, strengthen insulation, or improve resilience of the fiber. Instead, the water introduces issues that compromise these essential functions, leading to the conclusion that it makes the core less effective for its intended purpose.