A properly balanced hot tub can last three to four months between drain and fills, depending on use. But, as more chemicals are added to the water, the water becomes saturated. Water evaporation increases the concentration of chemicals in the water, adding to the saturation as well. Over time, the more the water becomes saturated with chemicals, the chemicals become less effective. This increase in the Total Dissolved Solids can cause your filter to need cleaning more often and reducing the energy efficiency of the heater, too. See how easy it is to drain and refill your hot tub water.