1st-line wrote:Slightly off topic.... how does the water taste on dual boiler machines that have large dedicated boilers for espresso extraction?

I've tested this on my Reneka Techno, which has 1.4 liter boilers for both brew and steam, with the steam boiler being fed from the brew boiler. I've done it in the usual fashion, by running water into a cup, letting it cool, and tasting it. The results are interesting: both boilers are of identical construction, with a copper tube captured by brass end plates, but the water from the brew boiler, which is completely full, never picks up a taste, while the water from the steam boiler, which is partially full, goes stale enough that I wouldn't use it for anything except heating cups. The steam also picks up a taste if I don't do any steaming for a day or so.

Best,
David

There are two issues regarding the water in dual boiler machines: water for espresso brewing should be fresh, while the water in the steam/hot water boiler doesn't need to be fresh, even for an americano - I believe.

The reservoir in my old Brewtus II began to look and smell like a neglected fish tank after about a month. I believe its proximity to the hot boiler had a lot to do with that.