How much your hot tub takes to run will depend on its size, water capacity and how much you use it. Providing you don’t come into any additional spending on repairs or replacements, a good-quality hot tub should cost you no more than £30-£40 per month, according to hot tub brand Aqua Warehouse. This is for an average four-person hot tub of a 700 litre capacity. Though to put it simply, the more you use the hot tub the more energy and water you will use.