SLF Water Filtration Comparison · 2026
RKIN Flash RO
Good fit for shoppers prioritizing a compact traditional under-sink RO system with optional remineralization and no electricity requirement.
VIVA21 5-Stage RO
Recommended for shoppers seeking an affordable traditional under-sink RO system with stronger certification positioning than many budget alternatives.
VIVA21 5-Stage RO
Choose the VIVA21 5-Stage for low purchase and maintenance costs.
RO Performance & Ownership
Compare RO output, filtration stages, remineralization, contaminant evidence, certifications and ownership cost.
Which Is Right for You?
RKIN Flash RO
Best for: Households wanting a compact under-sink reverse-osmosis system with strong filtration and the option to remineralize the purified water.
Consider if: Want Remineralization
VIVA21 5-Stage RO
Best for: Budget-conscious households that want a conventional, certified-positioned under-sink RO system with a storage tank and standard-size replacement filters.
Consider if: Budget Under $200, Low Replacement Cost
Our Recommendation
RKIN Flash RO
A flexible traditional under-sink RO option, especially for buyers who value non-electric operation and selectable post-filtration.
VIVA21 5-Stage RO
A strong budget-oriented conventional RO choice for households that have cabinet space and value certification and standard replacement filters over high output and connected features.
The Short Answer
Choose the AlcaPure version for calcium/magnesium remineralization and alkaline 7-8 pH.
Choose the VIVA21 5-Stage for low purchase and maintenance costs.
Water Filter Comparison FAQs
Answers are generated from the current SLF product records for these two systems.
Which is better, RKIN Flash RO or VIVA21 5-Stage RO?
VIVA21 5-Stage RO is the overall pick for this specific matchup. Choose the VIVA21 5-Stage for low purchase and maintenance costs.
Which system has the higher daily filtration capacity?
RKIN Flash RO has the higher rated output: 75 GPD versus 50 GPD.
Which system offers remineralization?
RKIN Flash RO: Yes. VIVA21 5-Stage RO: No.
Which system has the lower MSRP?
VIVA21 5-Stage RO has the lower MSRP in the current SLF records at $289.99, compared with $499.95 for the other system.
Do both systems require a plumbing connection?
RKIN Flash RO: Yes. VIVA21 5-Stage RO: Yes.
Which system is more renter friendly?
RKIN Flash RO: No. VIVA21 5-Stage RO: No. Check lease and plumbing-modification rules before installing an under-sink system.
What certifications are listed for these systems?
RKIN Flash RO: RKIN states that the 75 GPD reverse osmosis membrane used in the Flash system is NSF/ANSI 58 certified. This is component-level evidence for the RO membrane; exact-model NSF/ANSI 58 certification of the complete Flash RO system was not confirmed. VIVA21 5-Stage RO: Filter United identifies exact model V21RS5S01 as WQA Gold Seal certified to NSF/ANSI 58 for reverse-osmosis system performance and NSF/ANSI/CAN 372 for lead-content compliance. SLF has not independently located the exact model in WQA's searchable public directory, so retain the manufacturer-source qualification until the directory record is captured.
How do estimated annual filter costs compare?
RKIN Flash RO: $145.44. VIVA21 5-Stage RO: $60.00. Actual replacement timing and prices can vary.