Complex sentence: The top of the water tank is usually closed to prevent vapour from infiltrating the banya, and water to be thrown on the rocks should be taken from the tank as this will make better steam than if cold water were used.
Split into simpler sentences: The top of the water tank is usually closed to prevent vapour from infiltrating the banya. Water to be thrown on the rocks should be taken from the tank as this will make better steam than if cold water were used.