What is the primary function of a water heater?

The primary function of a water heater is to heat water for domestic and commercial use. Water heaters are designed to provide hot water for various applications, such as bathing, cooking, cleaning, and space heating. They operate by utilizing energy sources like electricity, gas, or solar power to elevate the temperature of water to the desired level. This functionality is essential in homes and businesses, ensuring that hot water is readily available for everyday tasks.

Other options presented do not align with the primary purpose of a water heater. For example, cooling water is not a function associated with water heaters, as they are specifically designed to increase water temperature. Additionally, purifying water for drinking is typically the role of water filtration systems, not water heaters. Storing water for irrigation also falls outside the scope of a water heater's intended use, which focuses on heating rather than storage. Therefore, option C correctly identifies the main purpose of a water heater.