Opal can make good nugget ice with typical city water, this is water that is 12gpg hardness or less (205ppm hardness). Hard water consists of dissolved minerals such as calcium and magnesium; it can leave deposits on the inside of your Opal, reducing its performance over time. Very hard water (>12gpg) is also more difficult to freeze, further reducing performance. While a filter can remove suspended solids and improve water taste, it cannot remove hardness.
Well water and spring water can contain more dissolved minerals than city water. Because water softeners exchange one mineral for another, softened water may not improve water conditions in regards to making ice. Water with a high mineral content has a lower freezing point. When Opal makes ice with this type of water, the nuggets tend to be softer and slushier. In some cases, the ice nuggets will not come out of the upper area of the ice maker and it goes into a fault condition called Defrost Mode. We recommend you make ice with distilled water, or a mixture of distilled water and tap water, which should improve Opal’s ice making performance.