Ever wonder about why you top the water up in your hot tub more frequently in the winter? Or if you have a small leak due to filling more frequently during the winter? Water evaporates in dryer air faster. In a hot tub the water is warm which also contributes to quicker evaporation. Another large factor is how much the hot tub is being used, at what temperature and by how many people. You will have water loss due to spill over, as well as what is held in the bathing suit. Also the temperature you keep your spa and how long you use it plays a factor in evaporation along with how strong the wind is. The wind can play a huge factor in water loss.
That being said, it’s always good to check around the base of your hot tub to determine if there are wet spots as well as to remove the access panel to see if you have a leak if you water seems to be going done inches per day.