Under-sink reverse osmosis systems, ranked

Start with what the system is certified to reduce, not what the box claims. A certification is a listing in a certifier's own database naming the model and the standard; a claim is a sentence on the packaging. The two are not the same thing and the gap between them is where most of this category's marketing lives.

Then price the filters, not the system. Replacement cartridges over five years routinely cost more than the unit, and a system whose replacement interval the brand declines to publish is worse to own than one that prints it on the box.

Last, measure the cabinet. Reverse osmosis systems need a drain connection and front clearance to change the cartridges, and a system that does not fit is not a bargain at any price.

Every system is scored out of 10 on four weighted components: certified coverage (40), claim integrity (20), cost of ownership (25), practical fit (15). Commission never enters the ranking — the scoring code is handed a record with the commerce block stripped out, so it cannot read a commission rate even if one existed.