Deer consume more water than any other mineral (water is a mineral, a naturally occurring substance). The amount of water deer need increases during hot and dry periods in summer. Where good water is abundant, no big deal. But where water is limited either by quantity or quality, some of a deer’s bodily functions are limited, such as transferring calcium to growing antlers or milk production for fawns.
Deer travel to find water. But if they are forced out of their home range in search of H2O, bucks and does expend huge amounts of energy that then can’t be used for other bodily processes like antler growth and milk production. Biologists point out that deer traveling out of their range to find water is very rare, except possibly during an extended drought. Normally they can find enough water to survive in their core areas.
Whitetails are adaptable and resilient, and are used to dealing with natural hardships and stress. An extended drought and abnormally hot summer in your region might lead to smaller antler growth and less fawn recruitment that fall. But a typical summer with periods of high heat and dry weeks won’t affect the herd much.