Soft water (nansui)
軟水なんすいSoft water (nansui) is water with a low content of metal ions such as calcium and magnesium. Under the World Health Organization (WHO) standard, water with a calcium concentration of 60 ppm or less is generally considered soft. Because it contains fewer of these minerals than hard water, soft water has a gentle mouthfeel and is easy to drink.
In sake brewing, soft water is often preferred. It supports the activity of the yeast and helps flavor components to be drawn out more easily during the brewing process. For example, Raiden-sama no Shimizu, the water used by Hakkai Jozo, is an ultra-soft water with a hardness of about 2, and this gentle water is regarded as a factor in creating the delicate character of its sake.