Dishwasher and detergent manufacturers recommend that customers call their water utility in order to optimize detergent use. The City's water is between 7 and 8 GPG (Grains Per Gallon) of hardness. Expressed as calcium carbonate equivalent, this is about 128 PPM (Parts Per Million). On dishwasher charts, this usually is rated as "moderately hard" water. This is the natural hardness of Lake Michigan water, which is derived from the limestone in the lake bed. The City's water treatment does not affect hardness.