Six-Stage Reverse Osmosis

What I have

A six-stage under-sink reverse osmosis system. Everything I drink and everything I cook with comes through it.

Why RO rather than carbon

Because it is the broadest thing available at a sink. A carbon block handles taste, chlorine and a set of organics. RO handles those plus dissolved solids, heavy metals, fluoride, and much of what carbon passes straight through.

The tradeoff is real: it strips minerals along with everything else, and it wastes water sending the concentrate down the drain. The mineral question is why the mineral water protocol puts salt back in. I would rather take everything out and choose what goes back in than filter selectively and hope the right things survived.

The part that decides whether it works at all

Changing the filters on schedule. A membrane past its life is decorative plumbing — it keeps producing water, the water keeps tasting fine, and it has stopped doing the job. This is the entire maintenance burden of the system and the only way it fails without telling you.