Carbon filters, positioned to remove chlorine and organic compounds, lose their absorptive capacity gradually and, unlike sediment filters, do not always show an obvious visible sign of exhaustion, making it easy to overlook their replacement schedule if not tracked separately. The reverse osmosis membrane itself has the longest typical service life among the components but is also the most expensive to replace, and its condition is usually assessed through water quality testing, such as total dissolved solids readings, rather than visual inspection alone, since membrane degradation affects purification quality before it affects flow rate noticeably.