The water in your hot tub should be changed approximately every six months. We often recommend doing this in the spring and the fall, to avoid any freezing problems. Most cities have by-laws that require you to put the water down the municipal water drain.  However, properly balanced water with a chlorine content below 3 parts per million should be safe for your grass. Additionally we recommend purchasing a 1/4 horsepower submersible pump to empty your tub. It will take approximately 40 minutes to drain most hot tubs this way, compared to several hours with the drain that the hot tub comes equipped with.