Typically, you should drain and refill your spa every three to four months. If you host a lot of hot tub parties or are a heavy user, you may need to drain your tub every other month. Determining what is right for your spa is a simple matter of testing your water on a weekly basis and keeping its pH levels balanced with spa chemicals. If the chemicals are doing their job, then draining your tub quarterly is adequate. If your water emits an odor or is foamy or gritty before three months have elapsed, more frequent drainage will be necessary.