Drinking water at the kitchen sink.
A whole-home system treats everything coming into the house. This is the opposite approach — one tap, taken much further. It sits under the kitchen sink with its own faucet and brings the water down to bottled quality for drinking, cooking, coffee and ice. Most families here end up wanting both, for different reasons.
Two ways to do it
Both use reverse osmosis and both mount under the sink on their own faucet. Where they part company is timing: one produces water the instant you ask for it, the other keeps a supply already made and waiting.
HW800 AlkaPro — Tankless
Seven stages, and nothing taking up the cabinet.
Water is purified as you draw it rather than sitting in a bladder tank waiting to be used, which gives you back most of the cupboard a conventional system occupies — up to 70% of it. It is also far less wasteful getting there, and the last stages put minerals back in, which is the difference between water that tastes clean and water that tastes like nothing at all.
Best for: crowded cabinets, less waste, and taste
Details and specs
5-Stage Tank RO
Five stages into a pressurised reserve.
The arrangement most people picture when they think of an under-sink RO, and there is nothing wrong with it. Water works through the cartridge stack and the membrane at its own pace and fills a pressurised tank; your faucet then draws from that reserve, so there is always some ready to pour.
Best for: anyone who prefers the conventional setup
Details and specsEither one pairs with any of the whole-home systems. They are solving different problems: the whole-home equipment is what protects the house, and this is what fixes the glass of water in your hand.
HW800 AlkaPro Tankless Reverse Osmosis
Tankless · 7-stage · alkaline
Going tankless removes the bulkiest component of a traditional setup. There is no bladder tank, so the unit reclaims up to 70% of the space one of those occupies under your sink, and with fewer fittings in the assembly there is simply less that can ever leak.
The seven stages
- Stage 1 5-micron polypropylene sediment pre-filter to take out suspended material.
- Stages 2–3 Double NSF carbon block filters to absorb chlorine by-products such as chloramine, THM and TCE, and to filter organic matter without releasing carbon fines. These also prepare the water before it reaches the RO membrane.
- Stage 4 NSF thin film composite RO membrane, 800 GPD — the stage that does the heavy lifting.
- Stage 5 In-line NSF coconut shell GAC filter to strip dissolved gases, taste and odor from the product water.
- Stage 6 Internal alkaline remineralizer — puts beneficial minerals back, balances the pH and is a large part of why the water tastes good rather than flat.
- Stage 7 A second in-line NSF coconut shell GAC filter as a final polish.
What that gets you
- 0.0001 micron filtration. The membrane is rated by its manufacturer at 95–99% rejection across a wide spectrum of impurities including total dissolved solids, heavy metals, microplastics and PFAS “forever chemicals”.
- 2:1 low drain ratio. Two cups of purified water for every one cup sent to drain — substantially less waste than a conventional RO system, which matters on a West Texas water bill.
- Automatic RO flush. The system washes trapped impurities off the membrane by itself, which prevents clogging and extends membrane life. The occasional flushing sound and blinking filter lights are it doing that.
- Lead-free water path built to NSF 372.
- DIY-friendly filter changes and a choice of faucet finishes and styles.
Certification
The HW800 AlkaPro is tested and certified by NSF International against NSF/ANSI Standard 58 for TDS reduction, and against that standard’s materials and structural integrity requirements. That certification covers TDS reduction specifically — the broader rejection figures above are the membrane manufacturer’s performance ratings rather than part of the NSF certification.
Specifications
| Filtration stages | 7-stage high-precision |
|---|---|
| Filtration precision | 0.0001 micron |
| System capacity | 800 GPD |
| Water flow rate | 0.53 GPM |
| Drain ratio | 2:1 |
| Design | Tankless — saves up to 70% under-sink space |
| Alkaline remineralization | Built in |
5-Stage Tank Reverse Osmosis
Conventional · storage tank
The traditional under-sink configuration, and one that has earned its reputation. A series of cartridges and an RO membrane do the filtering, feeding a pressurised storage tank that your dedicated faucet draws from — which means a reserve of purified water is always sitting ready.
The five stages
- Stage 1 5-micron polypropylene sediment pre-filter to extract suspended material.
- Stages 2–3 Double NSF carbon block filters to absorb heavy chlorine by-products such as chloramine, THM and TCE, and to filter organic matter without releasing carbon fines. These also prepare the water before it enters the RO element.
- Stage 4 NSF thin film composite RO membrane, 100 GPD. Rated by its manufacturer at 95–99% rejection across a wide spectrum of impurities including total dissolved solids and heavy metals.
- Stage 5 In-line NSF coconut shell GAC filter to remove dissolved gases, taste and odor from the product water.
Specifications
| Filtration stages | 5-stage |
|---|---|
| Membrane | NSF thin film composite, 100 GPD |
| Membrane rejection | 95–99% (manufacturer rating) |
| Design | Conventional — pressurized storage tank |
| Alkaline remineralization | Not included — see the AlkaPro |
The storage tank
The tank is a bigger part of how one of these performs than people expect, so it’s worth saying what’s in it:
- High-strength steel shell with corrosion-resistant construction.
- Food-grade butyl bladder that separates the stored water from the air charge, which prevents contamination and keeps the water fresh.
- Pre-pressurized sealed air chamber for consistent flow at the faucet, and less strain on the RO membrane — which extends the life of the whole system.
- Compact footprint with a reinforced heavy-duty base — fits under most kitchen sinks while still holding enough for drinking glasses, cooking, coffee and a refrigerator ice line.
Which should I get?
If the cupboard under your sink is already full, or you care about how little water gets wasted, or you want the extra stages and the remineralisation, the AlkaPro is the stronger system — and it is the one we most often pair with a whole-home system. If you would rather keep things conventional and have a tank of water already made, the 5-Stage Tank RO will serve you well for years.
Either pairs with any of the whole-home systems. Softening and filtering the whole house protects your plumbing and appliances; the drinking water system is what makes the glass in your hand taste right.
Backed the same way
Lifetime warranty on system dry parts, 5 years on the control valve, circuit board and filtration media, and 1 year on installation labor — full terms on the warranty page.