Yes, the SunnyTent really works that well. In the period from mid-May to late August, the temperature in the tent will rarely fall below 25 degrees. As a result, the water temperature is usually 25 degrees or higher. And without any additional heating. The brighter the sun, the more quickly the water warms up and to a higher temperature. The rate of warming up also depends on the initial temperature of the water and the amount of water. A small pool is warmed up quicker than a large pool. In fact, the SunnyTent works like a greenhouse, and like a greenhouse, the inner temperature is usually much higher than the outside temperature. Click here for the average temperatures as measured by several of our customers.