I plumbed in my first ice maker 10-15 years ago. The manual recommended not using softened water....
when I first started repairing fridges ice makers were the biggest problem, water quality from every public water supplier sucked bad, When they started putting filters on the fridges I quit putting 3-5 water valves on per day. the WS is another step to protect them.
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I'm WTF? I plumbed into the soft water and added a filter unit. It takes the froggy out of the ice as the tap water has a noticeable ammonia content we filter with a Brita pitcher Ammonia means nitrates so I guess we are well cured?