The relationship between temperature and the refractive index (RI) of water is minimal, with no direct correlation. Generally, the RI decreases as temperature increases, but the change is very slight. Specifically, the refractive index of water changes by less than 0.01% for each degree Celsius rise in temperature. This indicates that while there is a trend, it is not significant enough to have a major impact in practical applications. Understanding this relationship is important for precise optical measurements in varying temperatures.