That's about the only reason I could think of as well. Some machines, such as the Aurelia, mix boiler water with incoming cold water so the temperature is perfect and not alot of cold water has to be drawn in to replace the hot water being taken out. I do understand the dynamics of heat and metals used in espresso machines altering the chemical structure of water, but if the water is balanced to begin with scale shouldn't be much of an issue. I really don't think alot of people understand the importance of balanced water.
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