Choosing water filtration starts with a practical question: do you want a system that lives under the sink and uses reverse osmosis, or a countertop gravity system that keeps the filtration setup visible and separate from the sink cabinet? The four options here split clearly across those two approaches, with listed prices from USD 116.09 to USD 237.99. The lowest listed price is 51% below the highest, so the right choice depends on format, capacity, filter stages, and how much you want the system itself to do.
Quick take
- Best for high-output under-sink reverse osmosis: Waterdrop D6 Reverse Osmosis Water Filter, 600 GPD Under Sink Reverse Osmosis. It pairs a tankless design with a high daily capacity and smart faucet features.
- Best for alkaline-stage RO shoppers: 100 GPD 6 Stage Alkaline Reverse Osmosis Drinking Water Filter System Purifier. It adds a PH+ stage after the RO and post-carbon stages.
- Best for countertop gravity filtration: BLEMISHED Berkey Water Filter System w/ WQA Certified Boroux Black Filters. It is the only countertop gravity-style system in this group and includes two black filters in the title and attributes.
- Best lowest listed price: 5 Stage Undersink Reverse Osmosis Water Filter System 75 GPD Membrane Filter. It keeps to a simpler reverse osmosis setup and has the lowest price in the set.
Listed price comparison
| Product | Listed price | Price bar |
|---|---|---|
| 5 Stage Undersink Reverse Osmosis Water Filter System 75 GPD Membrane Filter | USD 116.09 | |
| 100 GPD 6 Stage Alkaline Reverse Osmosis Drinking Water Filter System Purifier | USD 135.99 | |
| Waterdrop D6 Reverse Osmosis Water Filter, 600 GPD Under Sink Reverse Osmosis | USD 179.00 | |
| BLEMISHED Berkey Water Filter System w/ WQA Certified Boroux Black Filters | USD 237.99 |
Decision matrix
Choose the Waterdrop D6 if: you want an under-sink reverse osmosis system with a tankless format, a built-in booster pump, a smart faucet with LED display, real-time TDS monitoring, and a filter life indicator. It is also the only Waterdrop-branded option here.
Choose the 100 GPD 6 Stage Alkaline system if: you want reverse osmosis plus an alkaline PH+ stage. Its filtration path includes pre-filters, an RO membrane, post carbon, and a final alkaline filter intended to add minerals such as calcium, potassium, and magnesium back to the water.
Choose the Berkey bundle if: you want a polished stainless steel gravity countertop system rather than an under-sink RO system. It is paired with Boroux black filters and is compatible with Berkey and Boroux models listed in its attributes.
Choose the 5 Stage Undersink RO system if: you want the simplest listed under-sink reverse osmosis choice in this comparison. It has five stages rather than the six-stage alkaline Simpure option and is the lowest-priced product here.
Concise product notes
Waterdrop D6 Reverse Osmosis Water Filter, 600 GPD Under Sink Reverse Osmosis
The Waterdrop D6 is the strongest fit for shoppers prioritizing output and compact under-sink placement. Its title and attributes center on 600 GPD reverse osmosis, while the description adds a tankless design, built-in booster pump, smart faucet, TDS monitoring, and filter life indicator. That makes it more feature-packed than the two Simpure under-sink RO systems. The limitation is that it is listed as Certified - Refurbished rather than New, and it requires an electrical outlet for operation. It also sits above both Simpure systems on listed price, so the extra features matter most if you specifically want its high-flow, tankless configuration.
100 GPD 6 Stage Alkaline Reverse Osmosis Drinking Water Filter System Purifier
This Simpure system is the better match if the phrase "6 Stage Alkaline" is central to your search. The filtration sequence includes sediment, GAC, CTO, reverse osmosis, post carbon, and a PH+ alkaline filter, so it has one more stage than the other Simpure RO option. It is also marked New, with Universal compatible brand and model attributes. The tradeoff is that its stated capacity is much lower than the Waterdrop D6, and it costs more than the 5-stage Simpure system. Choose it when the alkaline stage is more important to you than getting the lowest listed price.
BLEMISHED Berkey Water Filter System w/ WQA Certified Boroux Black Filters
The Berkey bundle stands apart because it is not an under-sink reverse osmosis system. It is a polished stainless steel gravity countertop water filter system with two Boroux black filters, and the title specifically calls out WQA Certified Boroux Black Filters. The attributes list Crown (6g) capacity, carbon/charcoal filtration, open box condition, and compatibility with Berkey and Boroux models including BU2, TU2, CU2, and IU2. Its main limitation is price: it is the highest listed option in this group. It is also titled "BLEMISHED," so shoppers wanting a new under-sink RO unit will likely prefer one of the other three.
5 Stage Undersink Reverse Osmosis Water Filter System 75 GPD Membrane Filter
The 5-stage Simpure system is the cleanest choice for a lower-priced under-sink reverse osmosis setup. It includes the familiar pre-filter, RO membrane, and post-carbon structure, and its attributes list reverse osmosis filtration with 0.0001 micron filtration precision. It is marked New and uses Universal compatible brand and model attributes, matching the six-stage Simpure system on those compatibility cues. The limitation is that it does not include the alkaline PH+ stage found on the 100 GPD Simpure option, and its capacity is lower than both the Waterdrop D6 and the 100 GPD Simpure system. Its appeal is simplicity and the lowest listed price.
Final recommendation
For most shoppers comparing these four water filtration choices, start by deciding between under-sink reverse osmosis and countertop gravity filtration. If you want the countertop format, the BLEMISHED Berkey Water Filter System w/ WQA Certified Boroux Black Filters is the clear fit, though it also has the highest listed price at USD 237.99.
If you want under-sink reverse osmosis, the best all-around feature pick is the Waterdrop D6 Reverse Osmosis Water Filter, 600 GPD Under Sink Reverse Osmosis at USD 179.00 because it combines a tankless design, smart faucet features, and the highest GPD rating in this comparison. If you want an alkaline stage and a New condition listing, the 100 GPD 6 Stage Alkaline Reverse Osmosis Drinking Water Filter System Purifier at USD 135.99 is the more focused match. If price is the deciding factor, the 5 Stage Undersink Reverse Osmosis Water Filter System 75 GPD Membrane Filter at USD 116.09 is the straightforward pick and the lowest listed option by a meaningful margin.