Upgrading to this premium see-through Clear Housing on the first filter offers many advantages. Without opening the housing, you can easily monitor the filter's condition. You'll get an idea about your water's quality by looking at the color and speed of contaminant buildup on the filter cartridge.
Although the RO's 3 pre-filters normally last 12 months on most city water sources, they may need to be replaced sooner if your water source has heavy sediments and other contaminants.
So how do you know when to replace the pre-filters? Just look at the stage-1 prefilter -- when it turns from pure white to medium or dark brown, then you know it's time to replace the pre-filters.