hard water grout stains 3

https://phoenixvalleytilecleaninghaven.clearminster.com/posts/why-phoenix-valley-tile-cleaning-matters-for-arizona-homes

Hard water grout stains are those stubborn white or yellowish mineral deposits that build up on tile joints from repeated exposure to hard water, leaving the grout looking crusty, dull, and discolored over time, especially in showers and around sinks.