Throwing water on the stones is how you regulate heat and steam in the sauna. The shape, size and composition of the stones and the way they are arranged make all the difference. We recommend rounded stones because they provide a milder steam. Thanks to the rounded shape the water can reach inner layers of stones and evaporate gradually instead of evaporating all at once from the top layer. Since they are very visible in HUUM heaters, you need both smaller and bigger stones to avoid big noticeable gaps. We also suggest laying smaller stones and more close together on the top to accumulate the heat better.