How we make money. We earn a commission when you buy through links on this site, at no extra cost to you. Those commissions come from affiliate programmes run by the brands and by third-party networks, not from you.
How that affects this list. Products from brands we have a commercial relationship with are listed first. Products we earn little or nothing from can still appear, lower down, when they belong in the comparison.
How the order is set. The top three slots are named picks — best overall, most popular, best value — and each states the measurement it won on. Every product after them is ordered by one fixed formula: the Amazon star rating and review count, applied identically. No brand can pay for a slot, a badge or a score.
We do not test products in a lab. Read the full method on How We Rank.
1
2
Amazon's Choice
3
4
Amazon's Choice
5
6
Amazon's Choice
7
Amazon's Choice
8
9
10
This is the one that costs real money. Across the systems on this page we counted 1,557 mentions of leaking and only 29% were positive, and the complaint was not confined to the cheap end — Waterdrop, iSpring and SimPure all appear in it.
| Brand | Share of mentions that were positive | Sample |
|---|---|---|
| SimPure | 15% | 23 of 158 |
| iSpring | 30% | 361 of 1,194 |
| Waterdrop | 34% | 69 of 205 |
Under-sink systems hold mains pressure across several push-fit connections, and a joint that weeps rather than bursts can run for weeks behind a cupboard door before anyone notices. If the cabinet sits above a finished floor or a downstairs room, that changes what you should buy: a countertop unit holds no pressure and cannot flood anything. If you do go under-sink, run it for a week with a sheet of paper under each joint.
The 400, 600 or 800 GPD figure on the box is the membrane's daily throughput under ideal pressure and temperature. It tells you almost nothing about how fast your glass fills.
What governs that is whether the system has a tank. A tank system stores a few litres at low pressure and delivers them quickly, then needs time to recover. A tankless system filters on demand — no waiting for recovery, but the flow is whatever the pump can push, and it runs while you pour. Neither is faster in every situation, so pick on how you actually use water rather than on the largest number.
An RO membrane does not distinguish between contaminants and calcium. It strips almost everything, which is why RO water tastes flat to some people and why the question of whether it leaves you thirsty comes up so often.
The fix is a remineralising stage, sold as "alkaline" or "AK" on these listings, which adds a small amount of mineral back after filtering. Several systems here include it. It changes taste more than health — a normal diet supplies far more of these minerals than drinking water does — but if flat-tasting water would stop you using the thing, pay for the stage.
Every RO system produces wastewater: the concentrate that carries away what the membrane rejected. Older systems sent three or four litres to the drain for each litre they filtered. The tankless systems on this page are much better, typically quoted between 1:1 and 3:1.
It is worth knowing before you buy, both for the water bill and because it means an RO system is the wrong tool for filtering everything in the house. Plumb it to the drinking tap, not the whole supply.
A multi-stage system has several cartridges on different schedules — sediment and carbon stages every six to twelve months, the membrane every two years or so. Miss them and flow drops, taste returns, and the membrane fails early.
Add up a full replacement set and multiply by three years before comparing two systems. We found value-for-money mentions ran only 63% positive across 344 mentions, and running cost is where that disappointment usually comes from rather than the purchase itself.
WinnerReviews counted 1,557 mentions of leaking across the reverse osmosis systems on this page and only 29% of them were positive — the complaint shows up for Waterdrop, iSpring and SimPure alike. These units sit under a sink at mains pressure with several push-fit joints, so a slow leak is both the most common failure and the most expensive one. Whatever you buy, fit it where you would notice water, and check the joints in the first week.
453 of 1,557 mentions, 3 brands
Tankless systems trade the storage tank for a booster pump that runs each time you draw water. WinnerReviews found noise mentions for Waterdrop split almost evenly at 52% positive across 229 mentions. A tank system is quieter but takes up most of the cupboard; there is no option here that is both silent and compact.
119 of 229 mentions
The purchase price is not the price. Replacement filter sets are due every six to twenty-four months depending on the stage, and WinnerReviews found value-for-money mentions ran only 63% positive across 344 mentions on the systems where buyers raised it. Price the filter set before you buy the unit, not after.
218 of 344 mentions, 2 brands
