Filters should be changed on a regular basis
Six months for whole house cartidges, undersink carbon filters, and reverse osmosis pre-filters.
Twelve months for secondary cartridges and reverse osmosis post-filters.
Three years for reverse osmosis membranes. This depends on water quality and usage. When rejection rate drops below 80% membrane should be replaced. Bring filtered and unfiltered water samples in for free TDS test and rejection calculation or purchase your own TDS meter to measure membrane performance.