The sticker price is the lie. The filters are the subscription you never signed up for.
You buy an RO system once. You buy filters for as long as you own it. So the honest price of any system is: system price + 5 years of filters. Almost nobody does this math before buying. Let's do it now.
Proprietary cartridge systems: ~$80–150+/year in filters.
Universal 10-inch systems: ~$30–60/year.
That's the "one third" you keep hearing — measured against proprietary cartridges, the sealed kind only the maker sells. It's not marketing — it's just what happens when filters are a commodity instead of a monopoly. One honest caveat: standard-size brands like iSpring and APEC already use this universal format, and their sets cost about the same as any other universal cartridges. Nobody gets a third off there — the saving exists only against proprietary lock-in.
| Stage | Universal 10" price | Typical proprietary-brand price | Change every |
|---|---|---|---|
| PP sediment (5 micron) | $5–8 | $15–25 | 6 months |
| GAC carbon | $8–12 | $20–35 | 6–12 months |
| CTO carbon block | $10–15 | $25–40 | 6–12 months |
| RO membrane | $25–40 | $60–120 | 2–3 years |
| Post-carbon / alkaline | $8–12 | $20–35 | 12 months |
Prices move around — these are typical US retail ranges in 2026, not quotes. The pattern is what matters: every stage costs roughly 2–3x more as a proprietary brand cartridge, and the media inside is often made by the same handful of manufacturers.
| Item | Universal 10" system | Proprietary-cartridge system |
|---|---|---|
| System | $150–300 | $200–500 |
| 5 years of filters | ~$150–300 | ~$400–750 |
| 5-year total | ~$300–600 | ~$600–1,250 |
The system price difference is noise. The filter difference is the whole game. A "cheap" $200 proprietary system can easily become the most expensive option in your kitchen within three years.
Brand-name filters aren't a scam. You're paying for real things: their distribution network, certification paperwork, customer support, the convenience of one-click reorders and auto-ship reminders. Some of that is genuinely valuable. But you're also paying the lock-in margin — the premium a company can charge when you literally cannot buy the filter anywhere else. That part is pure rent.
We sell the universal kind, so of course we're going to look cheap here. Our subscription is $29 per 6 months (3× PP sediment + 2× CTO carbon block, free shipping) and single filters are $15 plus actual shipping. Check our current prices on the site — this guide shouldn't be your receipt. The point isn't that we're the cheapest; it's that any universal-filter system puts you in the $30–60/year band instead of the $80–150 band.
Proprietary cartridge systems typically run $80–150+ per year. Systems using universal 10-inch cartridges typically run $30–60 per year — roughly a third of the proprietary cost. Standard-size brands (iSpring, APEC) sell universal cartridges too, at prices in the same band; the gap is between proprietary and universal, not between brands.
The RO membrane is the priciest single cartridge ($25–40 universal, $60–120 branded), but it lasts 2–3 years. Of the stages you change annually, carbon blocks usually cost the most per cartridge.
Distribution, marketing, certification paperwork, and the convenience of matched auto-shipments — plus the margin that proprietary lock-in allows. The filter media itself often comes from the same manufacturers.
If your system uses standard 10" × 2.5" housings, yes — buy universal cartridges from any supplier. If it uses proprietary quick-change cartridges, you're limited to that brand's filters unless you switch systems.