Bees are like most animals in that they require water, but their uses for it may seem a little unusual.
Bees require water for two basic purposes: to dilute the brood food and to cool or air condition the hive. Water is not stored in the hive as is honey and pollen, but a small number of worker bees will keep some water in their honey stomachs as a sort of water reservoir for the colony. This water is mostly used to keep the larvae from drying out or becoming desiccated. These bees will place a drop of water in the cell with the brood when the temperatures are very high. The water used for cooling the hive and diluting the food is collected as needed by forager bees.
One of the commonly asked questions about honey bees is how do they know when to perform certain tasks. In the case of water collection the process is probably known. After forager bees collect nectar, they transfer it to a house bee when they return to the hive. The forager does not place the nectar directly into a cell in the hive. Thus the house bee has some control over what the forager collects. If the temperature goes above 92 degrees F in the hive, then it has become too high for the rearing of the brood. Under such conditions the house bees will more readily accept nectar that has a high water content over a nectar source that has a lower water content. This results in the foragers collecting more dilute nectar and some will begin to collect water.
The water that comes into the hives is distributed over the surfaces of the comb and the interior hive walls so that there is a thin layer of water. Other bees in the hive are fanning their wings to set up an air current and the current causes the water to evaporate which works like a water-cooled air conditioner. This process lowers the temperature in the hive and prevents heat damage to the developing larvae. The foragers will collect water as long as it is necessary for the cooling process to continue.
In desert areas where the temperature may rise above 100 degrees F a colony of honey bees may collect and evaporate over a gallon of water a day in order to cool the hive. To cool a hive bees will gather water and deposit it in droplets around the hive. A number of bees then join together, fan their wings and drive a large volume of air through the hive.