Why are water coolers not effective on rainy days?

Water coolers are often less effective on rainy days because high humidity levels can interfere with the cooling process. The moisture in the air can reduce the evaporation rate, which is essential for cooling the water. Additionally, cooler outdoor temperatures may mean that the water doesn't need to be cooled as much, leading to less demand for the cooler's functionality. Consequently, the overall efficiency and effectiveness of water coolers can diminish in such weather conditions.