Ideal coffee water is fresh and pure in taste and has no discernible odors. It should be mineral-rich, yet have a balanced mineral content. A total hardness of 7–12° EH, a carbonate hardness of 3–4° EH and a pH value of 6.5–7.5 are ideal (Source: ). Only then can coffee develop its full aroma.
Source: Deutscher Kaffeeverband
Read more about the meaning of EH or Eh, as chemical literature calls it, here.
What does this mean for anyone on a small island making coffee?
- Don’t use tap water!
- Don’t use water that has been desalinated!
- Don’t use Reverse Osmosis (RO) water!
- Don’t use just any mineral water but pay attention to pH and “dissolved minerals” per liter
If you do get RO water, get some tablets from Third Wave Water and you are fine!
Update: Chemists at MIT and 2 UK baristas have made a deep dive on this subject and analysed why soft water is particularly bad for making coffee.