The nozzle uses water from the main boiler of the machine. This is not where the groupheads get their water; they have their own, specialized boilers. The main boiler’s job is to produce steam to heat the grouphead boilers and power the steam wands. The water in the tank, while perfectly clean and healthy, cycles through the boiler very slowly and is re-boiled over and over under intense pressure.
Chemistry and thermodynamics are doing a number on the water in the boiler. When water is boiled over and over again, some compounds you need for extraction make their way out of solution, building up on the boiler walls, changing the mineral content of the remaining water*. You don’t directly control the temperature and pressure of the main boiler, or what’s happening to the water inside. Whatever qualities the water had when it entered the machine, the water that comes out of the hot-water tap could be something else entirely.
It’s an unknown, and you don’t want to make an americano or brew a tea with an unknown. Invest in a hot-water tower. Your drinks and your customers will thank you.
*For a more in-depth look at how water works and why you might want to think long and hard before using that hot water tap, check out Christopher Hendon’s article explaining how water works.
—Cory Eldridge is Fresh Cup‘s editor.