Water is an unusual liquid. In warm temperatures, the warmer more buoyant water will rise to the top of a tank and the cooler more dense water will sink to the bottom. In the winter, when water cools to its freezing point, it becomes lighter and floats to the top. As you heat up water from its freezing point, it gets heavier for the first few degrees and is at its densest at 4°C above freezing. It can all seem very counterintuitive! If you decide to use a heater inside your storage tank to prevent ice formation, you will have to overheat the water to make it buoyant enough to float to the top. This will require a lot of extra energy. By combining heating with active mixing, you can actually keep the tank ice-free during the winter and use substantially less energy.