Patna water carries fine suspended silt along with dissolved minerals, and the kitchen tap shows it before anything else does. The aerator fills, the flow drops, and the drop is gradual enough that most households adjust without registering it — a pot that used to fill in twenty seconds now takes forty and nobody notices the change.
On the surfaces, the same silt gives the deposit a greyish cast rather than the bright white crust of a hard water city, which is why people often think their tiles are simply stained.