At 295 ppm (17.3 grains per gallon), the Cal Am Dunnigan system is classified as extremely hard under the US Geological Survey scale, which puts anything above 180 ppm in the very hard category. For context, the Sacramento municipal supply runs well under 100 ppm. Dunnigan's Cal Am wells pull from the same valley aquifer geology that produces high mineral content throughout this stretch of the Sacramento Valley floor.
The 82.6% of residents on private wells are not covered by any public consumer confidence report, so their hardness is unknown without a lab test. The valley geology that produces hard water in the Cal Am wells affects the broader aquifer, making very hard well water plausible for most private supplies in the area — though individual wells vary by depth and location. If you are on a private well and have never tested it, a basic water quality panel covering hardness, iron, manganese and pH is worth running before selecting shower materials.
Hard water leaves its mark on bathrooms in two ways: white scale buildup on glass, fixtures and grout, and accelerated corrosion of chrome plating from the repeated wet-dry mineral cycling. At 295 ppm, untreated polished chrome fixtures will show visible deposits within a few weeks of installation. Standard clear frameless glass without a hydrophobic coating will cloud and haze within the same timeframe without daily squeegee maintenance. Standard cement grout in a light color will trap mineral staining that is nearly impossible to remove completely.
Our design response to Dunnigan water: acrylic wall panels with no grout lines to scale, brushed or matte black fixtures (the texture and color conceal deposits far better than polished finishes), factory-applied hydrophobic glass coatings as a standard spec rather than an option, epoxy grout wherever tile is used, and large-format tile that minimizes joint surface area. For homes on the Cal Am system, a whole-house or point-of-use water softener upstream of the shower supply is a worthwhile consideration — and an open wall during a remodel is the best time to rough in the plumbing for one.
Background reading: regrouting or retiling and easy-clean showerheads.