Why water cooler are not effective on a rainy day?

Water coolers are less effective on rainy days because the ambient humidity increases, making it harder for the cooler to evaporate water efficiently. The cooling process relies on the evaporation of water, which cools the air; high humidity reduces evaporation rates. Additionally, the damp conditions may lead to less usage of the cooler, as people often prefer to stay indoors and rely on other cooling methods.