When incoming water is hard/mineral-rich and is not being treated with a water softener by the customer, the hard water will be rough on the machine, its parts and can increase chemical consumption.

Calcium deposits have nothing to do with the stainless steel or the machine itself. It's a widely known problem that can cause issues not just for the machines and their parts but also resulting in reduced quality of laundered goods. For amplifying information, two independent sources are used.

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Additionally hard water will caused reduced wash chemical effectiveness leading to poor wash quality. Quoting from TEXTILE LAUNDERING TECHNOLOGY "The chemicals responsible for water hardness are calcium and magnesium salts and other less abundant salts of elements of the alkaline earth group. They're troublesome because they form insoluble compounds with soaps or reduce the effectiveness of synthetic detergents. The insoluble soaps formed tend to trap soil particles in the fabric, causing grayness. Also, they tend to oxidize, causing rancid odors on fabrics. Some types of water hardness cause scale in boilers, water heaters, and pipes, resulting in poor efficiency, increased maintenance and repair costs, and excessive fuel consumption."

Textile Laundering Technology by Charles L. Riggs, Ph.D. and Michael Klipper. copyright 2005 by Textile Rental Services Association of America