What the North Texas Municipal Water District's hardness numbers mean for Plano shower doors, faucets, dishwashers and kettles, and how to clean mineral film without damaging the surface underneath.
If your shower door turns cloudy a week after you scrub it, or your dishwasher leaves white spots on glasses, the cause comes from upstream. Plano and its neighbors buy treated water from the North Texas Municipal Water District, and the district itself describes that water as moderately hard.
This guide explains where the minerals come from, how to read the district's reports, and how to remove the film from each surface in a Plano home without etching or scratching it.
Plano was one of the ten original member cities when the state created the North Texas Municipal Water District in 1951, alongside McKinney. Richardson joined in 1973, Allen in 1998 and Frisco in 2001 as the 13th member. Today the district supplies more than 2.4 million people across 2,200 square miles.
The district draws from several reservoirs: Lavon Lake, its largest current source, plus Bois d'Arc Lake, Lake Texoma, Jim Chapman Lake and Lake Tawakoni. Its Wylie Water Treatment Plant treats a blend of Lavon Lake and Lake Texoma water, and the City of Frisco confirms that its treated water comes from the Wylie plant.
According to the district, the treated water is moderately hard mainly because of minerals in Lavon Lake. Those minerals are not a health concern, but they leave spots on dishes and lime scale on fixtures, which is the white crust every Plano homeowner eventually notices.
The district publishes monthly water quality reports for each treatment plant. In August 2026, treated water from the Wylie plant measured 116 to 128 parts per million of total hardness, expressed as calcium carbonate. The same report lists calcium at 35.1 to 41.6 parts per million and total dissolved solids at 332 to 397 parts per million.
Most dishwashers and water softeners ask for hardness in grains per gallon instead. The district's own instruction is to divide the hardness in milligrams per liter (the same as parts per million for water) by 17.12. That puts the August Wylie numbers at roughly 6.8 to 7.5 grains per gallon. Enter that setting in your dishwasher or softener so it doses rinse aid and salt correctly.
Hardness shifts with the lake blend and the season, so check the most recent report for the plant that supplies your city rather than relying on one month.
The basic chemistry is simple: mineral scale dissolves in mild acid. The skill is knowing where acid is safe.
The single most effective habit is drying wet surfaces. A squeegee on the shower door and a towel over the faucet after use remove the water before its minerals can deposit. Water that evaporates leaves its 332 to 397 parts per million of dissolved solids behind.
A recurring cleaning schedule keeps scale from building past the easy stage. Once a layer has been allowed to harden for months, it takes a One-Time Deep Clean, which includes treating shower glass for hard water spots and detailing faucets, to bring the surface back. Some Plano homeowners install water softeners; if you do, set them using the grains per gallon conversion above, and follow the maker's schedule for adding salt.
The district also changes one step of its treatment process for about 28 days each spring as routine maintenance. That does not change hardness, but it is a convenient yearly reminder to descale showerheads and aerators.
The questions Plano homeowners ask most often about this topic, answered plainly.
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