The Flash Undersink Reverse Osmosis System uses a multi-stage filtration process. Replacing filters on schedule keeps your water clean and your system running at full flow. Here is what to replace and when:
Every 6–12 Months
- Pre-Filter (Sediment + Carbon) — Traps sediment, chlorine, and other particles before they reach the membrane. Replace closer to 6 months on well water or high-sediment sources, or up to 12 months on municipal water supply.
- Post-Filter (Carbon Block or AlcaPure Alkaline) — Gives your water a final polish. The AlcaPure version also adds back healthy minerals for better taste and a higher pH.
Every 24 Months
- Reverse Osmosis Membrane — This is the core of the system. It removes up to 99% of total dissolved solids, including lead, fluoride, arsenic, and more. Replacing pre-filters on time protects the membrane and helps it last the full 2 years.
Signs It is Time for a Change
- Slower flow rate from your filtered water faucet
- Change in taste or smell of the filtered water
- TDS readings are climbing (if you use a TDS meter)
- It has been more than 12 months since your last filter change
Replacing Flash filters is straightforward — no tools required. The twist-on cartridges snap in and out in under a minute. You can find the complete replacement kit here: Flash Replacement Filters Kit.
If you are also looking for the post-filter separately, it is available here: Flash Post-Filter Replacement.
Questions about which filters you need? Reach out to us — we are happy to help.
Feb 14, 2026