Maintenance essentials / Filter United
Keep great-tasting water flowing with Filter United replacement filter sets. Choose universal-fit prefilters for compatible standard housings, or refresh more stages with our complete 5-stage and 6-stage alkaline sets.
Prefilters, complete 5-stage sets, and 6-stage alkaline options.
Clearly listed filter stages and components in every set.
Practical compatibility guidance and help from Filter United.
Your next filter change, simplified
From everyday prefilter maintenance to a full filtration refresh, find the set that matches the stages due for replacement. Check the contents and fit before adding to cart.
Model: V21RF5S12
Renew five filtration stages with sediment and carbon prefilters, a 50 GPD TFC RO membrane, and a coconut-shell post-carbon filter. Confirm membrane and connection fit.
Free shipping on order subtotals over $99 to the contiguous U.S. Shipping policy.
Model: V21RP3S06
Universal-fit cartridges for compatible standard 10 x 2.5 inch RO housings. Includes one sediment and two carbon block filters for stages 1-3; membrane and post-filter not included.
Free shipping on order subtotals over $99 to the contiguous U.S. Shipping policy.
Model: V21RF6S12PH
A complete six-stage refresh: prefilters, a 50 GPD TFC membrane, post-carbon filtration, and an alkaline remineralization stage. Match all stages to your existing system.
Free shipping on order subtotals over $99 to the contiguous U.S. Shipping policy.
Reverse osmosis replacement filters renew the consumable filtration stages in an existing RO system. A pre-filter set replaces sediment and carbon cartridges; a complete set can also include the RO membrane, post-carbon filter, and, where specified, alkaline media. Choose by system compatibility and included stages.
The Filter United approach
Refresh the components that do the work, with replacement sets designed around the VIVA21 filtration stages.
Sediment cartridges capture suspended particles. Carbon prefilters reduce chlorine, helping protect the downstream TFC membrane when maintained as directed.
Choose a prefilter set for stages 1-3, or a complete 5-stage or 6-stage set when those components are due. A complete set does not mean every stage needs the same replacement interval.
Send Filter United your system model, existing cartridge labels, and connection photos. We can help you review the listed specifications and select the appropriate replacement set.
Compatibility comes first
The V21RP3S06 pre-filter set uses the widely adopted 10 x 2.5 inch cartridge format. It gives owners of compatible standard under-sink RO systems a replacement option beyond their original brand. Match your housing and cartridge design to enjoy a straightforward stages 1-3 refresh. Membranes and inline post-filters have separate fit requirements.
Yes, the prefilter set can fit models from these brands when they accept the same standard 10 x 2.5 inch sediment and carbon cartridges. Confirm the exact model, housing size, and cartridge design before ordering. This cross-brand fit applies to the prefilter housings; proprietary quick-change, tankless, countertop, and specialty models may use other formats. Complete sets also need a separate membrane and fitting check. Brand names identify fit examples and do not imply affiliation.
Understand the stages
One 5-micron sediment cartridge and two 5-micron carbon block cartridges make up the VIVA21 prefilter set. They address particles and chlorine taste and odor before membrane treatment.
Complete sets include a 50 GPD thin-film composite membrane. Pressure-driven separation reduces dissolved salts; output varies with feed-water pressure, temperature, and dissolved-solids concentration.
The post-carbon filter polishes taste after RO treatment. The 6-stage set adds alkaline remineralization media; final mineral content and pH depend on water and operating conditions.
Maintain what you already own
Keep a replacement record by stage. Regular cartridge care helps you get continued use from your existing RO system.
Many conventional RO systems use a 6-12 month prefilter interval. Your system manual, source-water quality, and usage determine the appropriate schedule; replace sooner when required.
A change in taste or flow warrants inspection, but the absence of symptoms does not prove a filter is still effective. A TDS reading can help track membrane performance; it does not measure every contaminant.
Use current set prices and your actual replacement intervals to plan maintenance. Membranes, post-filters, and alkaline stages can have different service schedules.
Use a qualified technician when the procedure or connections are unfamiliar. Contact Filter United if you need help locating the correct instructions.
Choose with confidence
Clear answers about fit, included stages, and ongoing care.
Start with your system model and the stages due for service. Filter United offers a VIVA21 prefilter set for stages 1-3, a complete 5-stage set, and a complete 6-stage alkaline set. Review the contents on each product page and match cartridge, membrane, and connection specifications. Send us your model and filter-label photos if you want help checking fit.
No. The V21RP3S06 pre-filter set includes one sediment cartridge and two carbon block cartridges for stages 1-3. The V21RF5S12 and V21RF6S12PH complete sets list a 50 GPD TFC RO membrane and post-carbon filter; the 6-stage set also includes an alkaline stage. Choose the set that covers your planned maintenance.
Our V21RP3S06 pre-filter set is universal-fit for compatible standard 10 x 2.5 inch sediment and carbon housings used by many conventional under-sink RO systems. That means you can choose Filter United prefilters even if another brand made your system. Confirm your housing dimensions and cartridge design; proprietary quick-change formats are different. For complete sets, membrane and inline-filter fit must also be checked.
Follow the schedule for your installed system and each cartridge. A 6-12 month prefilter interval is common in conventional RO systems, but water quality and usage can call for earlier changes. Membranes and finishing stages have separate schedules. Keep a dated record and ask Filter United to help identify the replacement parts specified for your system.
Prefilters primarily address sediment and chlorine; the RO membrane is the principal stage for reducing dissolved salts. If TDS rises, check feed-water conditions, membrane condition, installation, and operating pressure. Filter United can help you identify the listed replacement components. A low TDS reading alone does not establish drinking-water safety.
Many standard housing-style systems allow cartridge changes with the appropriate tools and instructions. Follow your exact manual for shutoff, depressurization, sanitation, cartridge order, flushing, and leak checks. The artwork is an overview, not the full procedure. Contact Filter United for product guidance or use a qualified technician if you are unsure.
The V21RF6S12PH set includes an alkaline remineralization stage, but installation requires compatible space, connections, and system configuration. Adding a stage is not automatically a direct replacement for another model. Ask Filter United to review your setup first. Mineral content, taste, and final pH vary; a fixed pH or additional health benefit is not promised.
A system certification applies to the configuration, components, and claims identified in its certification listing. It should not be assumed to cover every replacement cartridge or another brand of system. Check the exact product documentation and approved replacement parts. Filter United can help you locate the information for your VIVA21 model.
Filter United · VIVA21 replacements
Find the replacement set for your next maintenance day.
