A common cause for weak water flow from a showerhead, even when the valve is fully open, is the accumulation of mineral deposits and impurities within the showerhead itself. This issue often occurs when water contains dissolved minerals, such as in hard water areas, which leave white residue around the small spray nozzles as water evaporates.
When these nozzles become partially blocked or narrowed by scale or debris, the water distribution becomes uneven, resulting in weak or misaligned spray patterns. If water pressure remains normal in other parts of the household, cleaning the showerhead nozzles is the recommended first step to restore performance.