As with the rice, some elements that can be found in water are good for the brewing process, others not.
Good elements, which help micro-organisms such as the yeast grow, are:
- Phosphoric acid
Negative elements are:
- Iron (colors the sake!)
- Manganese (same)
- Heavy metals (bad for humans)
- Ammonia and nitrous acid
- Wild yeasts
We also have to take into account the difference between hard and soft water. Hard water has a high mineral content (often the "good" minerals mentioned above), soft water much less so. In the Edo-period, sake brewers preferred relatively hard water, as the "good elements" in it helped the fermentation process, making it faster. In the Meiji-period, brewers discovered that it was also very much possible to brew excellent sake with soft water, only the technique should be different. Anyway, the Ginjo type sake - which became a technical possibility in the 20th century thanks to rice polishing by machines - should always be brewed slowly.
A famous example of hard water is the Miyamizu ("Temple water"), discovered 160 years ago in Nishinomiya by the Sakura-Masamune Brewery. This water contains little iron and mangan, but a lot of phosphoric acid, and also a relatively large amount of potassium and magnesium. The hard water gives a dry taste to the sake and that became characteristic of the sakes made in the Nada districts of Kobe. All breweries in the area started using this water, transporting it in casks to their premises. This "masculine" sake, as it was called, became very popular among the population of Edo, where it was shipped.
Excellent soft water can be found in the Fushimi ward of Kyoto or in Hiroshima Prefecture. Sakes from these areas are sweeter and have therefore been called "feminine."
Water is important for sake brewing - it is the only element that gives a clear local identity to the sake, as "terroir" in the case of grapes (sake rice nowadays is shipped all over Japan, and anyway, most of the typical local elements are lost during the polishing process). So the water drawn from local wells, is the only "terroir" for Sake!